document_title: Multivibrator

question_text: what is the other name of astable multivibrator

text: Multivibrator

text: History[edit]

text: The first multivibrator circuit, the classic astable multivibrator oscillator (also called a plate-coupled multivibrator) was first described by Henri Abraham and Eugene Bloch in Publication 27 of the French Ministère de la Guerre, and in Annales de Physique 12, 252 (1919). Since it produced a square wave, in contrast to the sine wave generated by most other oscillator circuits of the time, its output contained many harmonics above the fundamental frequency, which could be used for calibrating high frequency radio circuits. For this reason Abraham and Bloch called it a multivibrateur. It is a predecessor of the Eccles-Jordan trigger[7] which was derived from the circuit a year later.

text: Historically, the terminology of multivibrators has been somewhat variable:

text:
1942 – multivibrator implies astable: "The multivibrator circuit (Fig. 7-6) is somewhat similar to the flip-flop circuit, but the coupling from the anode of one valve to the grid of the other is by a condenser only, so that the coupling is not maintained in the steady state."[8]
1942 – multivibrator as a particular flip-flop circuit: "Such circuits were known as 'trigger' or 'flip-flop' circuits and were of very great importance. The earliest and best known of these circuits was the multivibrator."[9]
1943 – flip-flop as one-shot pulse generator: "It should be noted that an essential difference between the two-valve flip-flop and the multivibrator is that the flip-flop has one of the valves biased to cutoff."[10]
1949 – monostable as flip-flop: "Monostable multivibrators have also been called 'flip-flops'."[11]
1949 – monostable as flip-flop: "... a flip-flop is a monostable multivibrator and the ordinary multivibrator is an astable multivibrator."[12]

text: Astable multivibrator[edit]

text: An astable multivibrator consists of two amplifying stages connected in a positive feedback loop by two capacitive-resistive coupling networks.[not in citation given] The amplifying elements may be junction or field-effect transistors, vacuum tubes, operational amplifiers, or other types of amplifier. Figure 1, below right, shows bipolar junction transistors.

text: The circuit is usually drawn in a symmetric form as a cross-coupled pair. The two output terminals can be defined at the active devices and have complementary states. One has high voltage while the other has low voltage, except during the brief transitions from one state to the other.

text: Operation[edit]

text: The circuit has two astable (unstable) states that change alternatively with maximum transition rate because of the "accelerating" positive feedback. It is implemented by the coupling capacitors that instantly transfer voltage changes because the voltage across a capacitor cannot suddenly change. In each state, one transistor is switched on and the other is switched off. Accordingly, one fully charged capacitor discharges (reverse charges) slowly thus converting the time into an exponentially changing voltage. At the same time, the other empty capacitor quickly charges thus restoring its charge (the first capacitor acts as a time-setting capacitor and the second prepares to play this role in the next state). The circuit operation is based on the fact that the forward-biased base-emitter junction of the switched-on bipolar transistor can provide a path for the capacitor restoration.

text: State 1 (Q1 is switched on, Q2 is switched off)

text: In the beginning, the capacitor C1 is fully charged (in the previous State 2) to the power supply voltage V with the polarity shown in Figure 1. Q1 is on and connects the left-hand positive plate of C1 to ground. As its right-hand negative plate is connected to Q2 base, a maximum negative voltage (-V) is applied to Q2 base that keeps Q2 firmly off. C1 begins discharging (reverse charging) via the high-value base resistor R2, so that the voltage of its right-hand plate (and at the base of Q2) is rising from below ground (-V) toward +V. As Q2 base-emitter junction is reverse-biased, it does not conduct, so all the current from R2 goes into C1. Simultaneously, C2 that is fully discharged and even slightly charged to 0.6 V (in the previous State 2) quickly charges via the low-value collector resistor R4 and Q1 forward-biased base-emitter junction (because R4 is less than R2, C2 charges faster than C1). Thus C2 restores its charge and prepares for the next State C2 when it will act as a time-setting capacitor. Q1 is firmly saturated in the beginning by the "forcing" C2 charging current added to R3 current. In the end, only R3 provides the needed input base current. The resistance R3 is chosen small enough to keep Q1 (not deeply) saturated after C2 is fully charged.

text: When the voltage of C1 right-hand plate (Q2 base voltage) becomes positive and reaches 0.6 V, Q2 base-emitter junction begins diverting a part of R2 charging current. Q2 begins conducting and this starts the avalanche-like positive feedback process as follows. Q2 collector voltage begins falling; this change transfers through the fully charged C2 to Q1 base and Q1 begins cutting off. Its collector voltage begins rising; this change transfers back through the almost empty C1 to Q2 base and makes Q2 conduct more thus sustaining the initial input impact on Q2 base. Thus the initial input change circulates along the feedback loop and grows in an avalanche-like manner until finally Q1 switches off and Q2 switches on. The forward-biased Q2 base-emitter junction fixes the voltage of C1 right-hand plate at 0.6 V and does not allow it to continue rising toward +V.

text: State 2 (Q1 is switched off, Q2 is switched on)

text: Now, the capacitor C2 is fully charged (in the previous State 1) to the power supply voltage V with the polarity shown in Figure 1. Q2 is on and connects the right-hand positive plate of C2 to ground. As its left-hand negative plate is connected to Q1 base, a maximum negative voltage (-V) is applied to Q1 base that keeps Q1 firmly off. C2 begins discharging (reverse charging) via the high-value base resistor R3, so that the voltage of its left-hand plate (and at the base of Q1) is rising from below ground (-V) toward +V. Simultaneously, C1 that is fully discharged and even slightly charged to 0.6 V (in the previous State 1) quickly charges via the low-value collector resistor R1 and Q2 forward-biased base-emitter junction (because R1 is less than R3, C1 charges faster than C2). Thus C1 restores its charge and prepares for the next State 1 when it will act again as a time-setting capacitor...and so on... (the next explanations are a mirror copy of the second part of State 1).

text: Multivibrator frequency[edit]

text: Derivation[edit]

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text: The duration of state 1 (low output) will be related to the time constant R2C1 as it depends on the charging of C1, and the duration of state 2 (high output) will be related to the time constant R3C2 as it depends on the charging of C2. Because they do not need to be the same, an asymmetric duty cycle is easily achieved.

text: The voltage on a capacitor with non-zero initial charge is:

text: Looking at C2, just before Q2 turns on, the left terminal of C2 is at the base-emitter voltage of Q1 (VBE_Q1) and the right terminal is at VCC ("VCC" is used here instead of "+V" to ease notation). The voltage across C2 is VCC minus VBE_Q1 . The moment after Q2 turns on, the right terminal of C2 is now at 0 V which drives the left terminal of C2 to 0 V minus (VCC - VBE_Q1) or VBE_Q1 - VCC. From this instant in time, the left terminal of C2 must be charged back up to VBE_Q1. How long this takes is half our multivibrator switching time (the other half comes from C1). In the charging capacitor equation above, substituting:

text: results in:

text: Solving for t results in:

text: For this circuit to work, VCC>>VBE_Q1 (for example: VCC=5 V, VBE_Q1=0.6 V), therefore the equation can be simplified to:

text: The period of each half of the multivibrator is therefore given by t = ln(2)RC.

text: The total period of oscillation is given by:

text: T = t1 + t2 = ln(2)R2 C1 + ln(2)R3 C2

text:
f
=

1
T

=

1

ln

(
2
)
⋅
(

R

2

C

1

+

R

3

C

2

)

≈

1

0.693
⋅
(

R

2

C

1

+

R

3

C

2

)

{\displaystyle f={\frac {1}{T}}={\frac {1}{\ln(2)\cdot (R_{2}C_{1}+R_{3}C_{2})}}\approx {\frac {1}{0.693\cdot (R_{2}C_{1}+R_{3}C_{2})}}}

text: where...

text:
f is frequency in hertz.
R2 and R3 are resistor values in ohms.
C1 and C2 are capacitor values in farads.
T is the period (In this case, the sum of two period durations).

text: For the special case where

text:
t1 = t2 (50% duty cycle)
R2 = R3
C1 = C2

text:
f
=

1
T

=

1

ln

(
2
)
⋅
2
R
C

≈

0.72

R
C

{\displaystyle f={\frac {1}{T}}={\frac {1}{\ln(2)\cdot 2RC}}\approx {\frac {0.72}{RC}}}

[13]

text: Output pulse shape[edit]

text: The output voltage has a shape that approximates a square waveform. It is considered below for the transistor Q1.

text: During State 1, Q2 base-emitter junction is reverse-biased and capacitor C1 is "unhooked" from ground. The output voltage of the switched-on transistor Q1 changes rapidly from high to low since this low-resistive output is loaded by a high impedance load (the series connected capacitor C1 and the high-resistive base resistor R2).

text: During State 2, Q2 base-emitter junction is forward-biased and capacitor C1 is "hooked" to ground. The output voltage of the switched-off transistor Q1 changes exponentially from low to high since this relatively high resistive output is loaded by a low impedance load (capacitor C1). This is the output voltage of R1C1 integrating circuit.

text: To approach the needed square waveform, the collector resistors have to be low in resistance. The base resistors have to be low enough to make the transistors saturate in the end of the restoration (RB < β.RC).

text: Initial power-up[edit]

text: When the circuit is first powered up, neither transistor will be switched on. However, this means that at this stage they will both have high base voltages and therefore a tendency to switch on, and inevitable slight asymmetries will mean that one of the transistors is first to switch on. This will quickly put the circuit into one of the above states, and oscillation will ensue. In practice, oscillation always occurs for practical values of R and C.

text: However, if the circuit is temporarily held with both bases high, for longer than it takes for both capacitors to charge fully, then the circuit will remain in this stable state, with both bases at 0.60 V, both collectors at 0 V, and both capacitors charged backwards to −0.60 V. This can occur at startup without external intervention, if R and C are both very small.

text: Frequency divider[edit]

text: An astable multivibrator can be synchronized to an external chain of pulses. A single pair of active devices can be used to divide a reference by a large ratio, however, the stability of the technique is poor owing to the variability of the power supply and the circuit elements. A division ratio of 10, for example, is easy to obtain but not dependable. Chains of bistable flip-flops provide more predictable division, at the cost of more active elements.[13]

text: Protective components[edit]

text: While not fundamental to circuit operation, diodes connected in series with the base or emitter of the transistors are required to prevent the base-emitter junction being driven into reverse breakdown when the supply voltage is in excess of the Veb breakdown voltage, typically around 5-10 volts for general purpose silicon transistors. In the monostable configuration, only one of the transistors requires protection.

text: Astable multivibrator using an op-amp[edit]

text:
Assume all the capacitors to be discharged at first. The output of the op-amp Vo at node c is +Vsat initially. At node a, a voltage of +β Vsat  is formed due to voltage division where

β
=

[

R
2

R
1
+
R
2

]

{\displaystyle \beta =\left[{\frac {R2}{R1+R2}}\right]}

. The current that flows from nodes c and b to ground charges the capacitor C towards +Vsat. During this charging period, the voltage at b becomes greater than +β Vsat at some point. The voltage at inverting terminal will be greater than the voltage at the non-inverting terminal of the op-amp. This is a comparator circuit and hence, the output becomes -Vsat. The voltage at node a becomes -βVsat due to voltage division. Now the capacitor discharges towards -Vsat. At some point, the voltage at b becomes less than -β Vsat. The voltage at the non-inverting terminal will be greater than the voltage at the inverting terminal of the op-amp. So, the output of the op-amp is +Vsat. This repeats and forms a free-running oscillator or an astable multivibrator.

text: If VC is the voltage across the capacitor and from the graph, the time period of the wave formed at capacitor and the output would match, then the time period could be calculated in this way:

text:
V

c

=

V

c

(
∞
)
+
[

V

c

(
0
)
−

V

c

(
∞
)
]

e

−
t

R
C

{\displaystyle V_{c}=V_{c}(\infty )+[V_{c}(0)-V_{c}(\infty )]e^{\tfrac {-t}{RC}}}

text:
V

c

(
t
)
=

V

s
a
t

+
[
−
β

V

s
a
t

−

V

s
a
t

]

e

(

−
t

R
C

)

{\displaystyle V_{c}(t)=V_{sat}+[-\beta V_{sat}-V_{sat}]e^{\left({\frac {-t}{RC}}\right)}}

text: At t =T1,

text:
β

V

s
a
t

=

V

s
a
t

(
1
−
[
β
+
1
]

e

−
T
1

R
C

)

{\displaystyle \beta V_{sat}=V_{sat}(1-[\beta +1]e^{\tfrac {-T1}{RC}})}

text: Upon solving, we get:

text:
T
1
=
R
C
ln

[

1
+
β

1
−
β

]

{\displaystyle T1=RC\ln \left[{\frac {1+\beta }{1-\beta }}\right]}

text: We are taking values of R, C and β such that we get a symmetrical square wave. Thus, we get T1 = T2 and total time period T = T1 + T2. So, the time period of the square wave generated at the output is:

text:
T
=
2
R
C
ln

[

1
+
β

1
−
β

]

{\displaystyle T=2RC\ln \left[{\frac {1+\beta }{1-\beta }}\right]}

text: Monostable[edit]

text: In the monostable multivibrator, one resistive-capacitive network (C2-R3 in Figure 1) is replaced by a resistive network (just a resistor). The circuit can be thought as a 1/2 astable multivibrator. Q2 collector voltage is the output of the circuit (in contrast to the astable circuit, it has a perfect square waveform since the output is not loaded by the capacitor).

text: When triggered by an input pulse, a monostable multivibrator will switch to its unstable position for a period of time, and then return to its stable state. The time period monostable multivibrator remains in unstable state is given by t = ln(2)R2C1. If repeated application of the input pulse maintains the circuit in the unstable state, it is called a retriggerable monostable. If further trigger pulses do not affect the period, the circuit is a non-retriggerable multivibrator.

text: For the circuit in Figure 2, in the stable state Q1 is turned off and Q2 is turned on. It is triggered by zero or negative input signal applied to Q2 base (with the same success it can be triggered by applying a positive input signal through a resistor to Q1 base). As a result, the circuit goes in State 1 described above. After elapsing the time, it returns to its stable initial state.

text: Monostable using op-amp[edit]

text: The circuit is useful for generating single output pulse of adjustable time duration in response to a triggering signal. The width of the output pulse depends only on external components connected to the op-amp. A diode D1 clamps the capacitor voltage to 0.7 V when the output is at +Vsat. Let us assume that in the stable state the output Vo = +Vsat. The diode D1 clamps the capacitor to 0.7 V. The voltage at the non-inverting terminal through the potential divider will be + βVsat. Now a negative trigger of magnitude V1 is applied to the non-inverting terminal so that the effective signal at this terminal is less than 0.7 V. Then the output voltage switches from +Vsat to -Vsat. The diode will now get reverse biased and the capacitor starts charging exponentially to -Vsat through R. The voltage at the non-inverting terminal through the potential divider will be - βVsat. After some time the capacitor charges to a voltage more than - βVsat. The voltage on the non-inverting input is now greater than on the inverting input and the output of the op-amp switches again to +Vsat. The capacitor discharges through resistor R and charges again to 0.7 V.

text: The pulse width T of a monostable multivibrator is calculated as follows: The general solution for a low pass RC circuit is

text:
where

V

f

=
−

V

sat

{\displaystyle V_{f}=-V_{\text{sat}}}

 and

V

i

=

V

d

{\displaystyle V_{i}=V_{d}}

, the diode forward voltage. Therefore,

text:
at

t
=
T

{\displaystyle t=T}

,

text: after simplification,

text:
where

β
=

R
2

R
1
+
R
2

{\displaystyle \beta ={R2 \over R1+R2}}

text:
If

V

sat

>>

V

d

{\displaystyle V_{\text{sat}}>>V_{d}}

 and

R
1
=
R
2

{\displaystyle R1=R2}

 so that

β
=
0.5

{\displaystyle \beta =0.5}

, then

T
=
0.69
R
C

{\displaystyle T=0.69RC}

text: Bistable[edit]

text: In the bistable multivibrator, both resistive-capacitive networks (C1-R2 and C2-R3 in Figure 1) are replaced by resistive networks (just resistors or direct coupling).

text: This latch circuit is similar to an astable multivibrator, except that there is no charge or discharge time, due to the absence of capacitors. Hence, when the circuit is switched on, if Q1 is on, its collector is at 0 V. As a result, Q2 gets switched off. This results in more than half +V volts being applied to R4 causing current into the base of Q1, thus keeping it on. Thus, the circuit remains stable in a single state continuously. Similarly, Q2 remains on continuously, if it happens to get switched on first.

text: Switching of state can be done via Set and Reset terminals connected to the bases. For example, if Q2 is on and Set is grounded momentarily, this switches Q2 off, and makes Q1 on. Thus, Set is used to "set" Q1 on, and Reset is used to "reset" it to off state.


document_title: Plant

question_text: who divided up the living world into just plants and animals

question_tokens: who divided up the living world into just plants and animals

root

text: Plant

text: Definition

text: Plants are one of the two groups into which all living things were traditionally divided; the other is animals. The division goes back at least as far as Aristotle (384 BC – 322 BC), who distinguished between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when Linnaeus (1707–1778) created the basis of the modern system of scientific classification, these two groups became the kingdoms Vegetabilia (later Metaphyta or Plantae) and Animalia (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these organisms are still often considered plants, particularly in popular contexts.

tag: p

text: Outside of formal scientific contexts, the term "plant" implies an association with certain traits, such as being multicellular, possessing cellulose, and having the ability to carry out photosynthesis.[7][8]

text: Current definitions of Plantae

text: When the name Plantae or plant is applied to a specific group of organisms or taxon, it usually refers to one of four concepts. From least to most inclusive, these four groupings are:

text:
Name(s)
Scope
Description

Land plants, also known as Embryophyta
Plantae sensu strictissimo
Plants in the strictest sense include the liverworts, hornworts, mosses, and vascular plants, as well as fossil plants similar to these surviving groups (e.g., Metaphyta Whittaker, 1969,[9] Plantae Margulis, 1971[10]).

Green plants, also known as Viridiplantae, Viridiphyta or Chlorobionta
Plantae sensu stricto
Plants in a strict sense include the green algae, and land plants that emerged within them, including stoneworts. The names given to these groups vary considerably as of July 2011[update]. Viridiplantae encompass a group of organisms that have cellulose in their cell walls, possess chlorophylls a and b and have plastids that are bound by only two membranes that are capable of storing starch. It is this clade that is mainly the subject of this article (e.g., Plantae Copeland, 1956[11]).

Archaeplastida, also known as Plastida or Primoplantae
Plantae sensu lato
Plants in a broad sense comprise the green plants listed above plus Rhodophyta (red algae) and Glaucophyta (glaucophyte algae). This clade includes the organisms that eons ago acquired their chloroplasts directly by engulfing cyanobacteria (e.g., Plantae Cavalier-Smith, 1981[12]).

Old definitions of plant (obsolete)
Plantae sensu amplo
Plants in an ample sense refers to older, obsolete classifications that placed diverse algae, fungi or bacteria in Plantae (e.g., Plantae or Vegetabilia Linnaeus,[13] Plantae Haeckel 1866,[14] Metaphyta Haeckel, 1894,[15] Plantae Whittaker, 1969[9]).

tag: table

text: Another way of looking at the relationships between the different groups that have been called "plants" is through a cladogram, which shows their evolutionary relationships. The evolutionary history of plants is not yet completely settled, but one accepted relationship between the three groups described above is shown below.[16][17][18][19] Those which have been called "plants" are in bold.

text:
Archaeplastida

 Glaucophyta (glaucophyte algae)

 Rhodophyta (red algae)

Green plants

 Chlorophyta (part of green algae)

Streptophyta

 streptophyte algae (part of green algae)

 Charales (stoneworts, often included
in green algae)

 land plants or embryophytes

groups traditionally
included in the "algae"

text: The way in which the groups of green algae are combined and named varies considerably between authors.

text: Algae

text: Algae comprise several different groups of organisms which produce energy through photosynthesis and for that reason have been included in the plant kingdom in the past. Most conspicuous among the algae are the seaweeds, multicellular algae that may roughly resemble land plants, but are classified among the brown, red and green algae. Each of these algal groups also includes various microscopic and single-celled organisms. There is good evidence that some of these algal groups arose independently from separate non-photosynthetic ancestors, with the result that the brown algae, for example, are no longer classified within the plant kingdom as it is defined here.[20][21]

text: The Viridiplantae, the green plants – green algae and land plants – form a clade, a group consisting of all the descendants of a common ancestor. With a few exceptions among green algae, the green plants have the following features in common; cell walls containing cellulose, chloroplasts containing chlorophylls a and b, and food stores in the form of starch contained within the plastids. They undergo closed mitosis without centrioles, and typically have mitochondria with flat cristae. The chloroplasts of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic cyanobacteria.

text: Two additional groups, the Rhodophyta (red algae) and Glaucophyta (glaucophyte algae), also have chloroplasts that appear to be derived directly from endosymbiotic cyanobacteria, although they differ in the pigments which are used in photosynthesis from those of the Viridiplantae and so are different in colour. In these groups, the storage polysaccharide is floridean starch and is stored in the cytoplasm rather than in the plastids. These groups appear to have had a common origin with Viridiplantae and the three groups form the clade Archaeplastida, whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event. This is the broadest modern definition of the term 'plant'.

text: In contrast, most other algae (e.g. brown algae/diatoms, haptophytes, dinoflagellates, and euglenids) not only have different pigments but also have chloroplasts with three or four surrounding membranes. They are not close relatives of the Archaeplastida, presumably having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in even the broadest modern definition of the plant kingdom, although they were in the past.

text: The green plants or Viridiplantae were traditionally divided into the green algae (including the stoneworts) and the land plants. However, it is now known that the land plants evolved from within a group of green algae, so that the green algae by themselves are a paraphyletic group, i.e. a group that excludes some of the descendants of a common ancestor. Paraphyletic groups are generally avoided in modern classifications, so that in recent treatments the Viridiplantae have been divided into two clades, the Chlorophyta and the Streptophyta (including the land plants and Charophyta).[22][23]

text: The Chlorophyta (a name that has also been used for all green algae) are the sister group to the group from which the land plants evolved. There are about 4,300 species[24] of mainly marine organisms, both unicellular and multicellular. The latter include the sea lettuce, Ulva.

text: The other group within the Viridiplantae are the mainly freshwater or terrestrial Streptophyta, which consists of the land plants together with the Charophyta, itself consisting of several groups of green algae such as the desmids and stoneworts. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched.[23] The genus Spirogyra is a filamentous streptophyte alga familiar to many, as it is often used in teaching and is one of the organisms responsible for the algal "scum" so reprehensible to pond-owners. The freshwater stoneworts strongly resemble land plants and are believed to be their closest relatives.[citation needed] Growing in fresh water, they consist of a central stalk with whorls of branchlets, giving them a superficial resemblance to horsetails, species of the genus Equisetum, which are true land plants.

text: Fungi

text: The classification of fungi has been controversial until quite recently in the history of biology. Linnaeus' original classification placed the fungi within the Plantae, since they were unquestionably not animals or minerals and these were the only other alternatives. With later developments in microbiology, in the 19th century Ernst Haeckel felt that another kingdom was required to classify newly discovered micro-organisms. The introduction of the new kingdom Protista in addition to Plantae and Animalia, led to uncertainty as to whether fungi truly were best placed in the Plantae or whether they ought to be reclassified as protists. Haeckel himself found it difficult to decide and it was not until 1969 that a solution was found whereby Robert Whittaker proposed the creation of the kingdom Fungi. Molecular evidence has since shown that the most recent common ancestor (concestor), of the Fungi was probably more similar to that of the Animalia than to that of Plantae or any other kingdom.[25]

text: Whittaker's original reclassification was based on the fundamental difference in nutrition between the Fungi and the Plantae. Unlike plants, which generally gain carbon through photosynthesis, and so are called autotrophs, fungi generally obtain carbon by breaking down and absorbing surrounding materials, and so are called heterotrophic saprotrophs. In addition, the substructure of multicellular fungi is different from that of plants, taking the form of many chitinous microscopic strands called hyphae, which may be further subdivided into cells or may form a syncytium containing many eukaryotic nuclei. Fruiting bodies, of which mushrooms are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.

text: Diversity

text: The table below shows some species count estimates of different green plant (Viridiplantae) divisions. It suggests there are about 300,000 species of living Viridiplantae, of which 85–90% are flowering plants. (Note: as these are from different sources and different dates, they are not necessarily comparable, and like all species counts, are subject to a degree of uncertainty in some cases.)

text:
Diversity of living green plant (Viridiplantae) divisions

Informal group
Division name
Common name
No. of living species
Approximate No. in informal group

Green algae
Chlorophyta
green algae (chlorophytes)
3,800–4,300 [26][27]
8,500
(6,600–10,300)

Charophyta
green algae (e.g. desmids & stoneworts)
2,800–6,000 [28][29]

Bryophytes
Marchantiophyta
liverworts
6,000–8,000 [30]
19,000
(18,100–20,200)

Anthocerotophyta
hornworts
100–200 [31]

Bryophyta
mosses
12,000 [32]

Pteridophytes
Lycopodiophyta
club mosses
1,200 [21]
12,000
(12,200)

Pteridophyta
ferns, whisk ferns & horsetails
11,000 [21]

Seed plants
Cycadophyta
cycads
160 [33]
260,000
(259,511)

Ginkgophyta
ginkgo
1 [34]

Pinophyta
conifers
630 [21]

Gnetophyta
gnetophytes
70 [21]

Magnoliophyta
flowering plants
258,650 [35]

text: The naming of plants is governed by the International Code of Nomenclature for algae, fungi, and plants and International Code of Nomenclature for Cultivated Plants (see cultivated plant taxonomy).

text: Evolution

text: The evolution of plants has resulted in increasing levels of complexity, from the earliest algal mats, through bryophytes, lycopods, ferns to the complex gymnosperms and angiosperms of today. Plants in all of these groups continue to thrive, especially in the environments in which they evolved.

text: An algal scum formed on the land 1,200 million years ago, but it was not until the Ordovician Period, around 450 million years ago, that land plants appeared.[36] However, new evidence from the study of carbon isotope ratios in Precambrian rocks has suggested that complex photosynthetic plants developed on the earth over 1000 m.y.a.[37] For more than a century it has been assumed that the ancestors of land plants evolved in aquatic environments and then adapted to a life on land, an idea usually credited to botanist Frederick Orpen Bower in his 1908 book "The Origin of a Land Flora". A more recent alternative view, supported by genetic evidence, is that they evolved from single-celled algae that were already terrestrial.[38] Primitive land plants began to diversify in the late Silurian Period, around 420 million years ago, and the fruits of their diversification are displayed in remarkable detail in an early Devonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs. By the middle of the Devonian Period most of the features recognised in plants today are present, including roots, leaves and secondary wood, and by late Devonian times seeds had evolved.[39] Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees. Evolutionary innovation continued after the Devonian period. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the evolution of flowering plants in the Triassic (~200 million years ago), which exploded in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around 40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low CO2 and warm, dry conditions of the tropics over the last 10 million years.

text: A 1997 proposed phylogenetic tree of Plantae, after Kenrick and Crane,[40] is as follows, with modification to the Pteridophyta from Smith et al.[41] The Prasinophyceae are a paraphyletic assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta:[42] later authors have not followed this suggestion.

text:
Prasinophyceae (micromonads)

Streptobionta

Embryophytes

Stomatophytes

Polysporangiates

Tracheophytes

Eutracheophytes

Euphyllophytina

Lignophyta

Spermatophytes (seed plants)

Progymnospermophyta †

Pteridophyta

Pteridopsida (true ferns)

Marattiopsida

Equisetopsida (horsetails)

Psilotopsida (whisk ferns & adders'-tongues)

Cladoxylopsida †

Lycophytina

Lycopodiophyta

Zosterophyllophyta †

Rhyniophyta †

Aglaophyton †

Horneophytopsida †

Bryophyta (mosses)

Anthocerotophyta (hornworts)

Marchantiophyta (liverworts)

Charophyta

Chlorophyta

Trebouxiophyceae (Pleurastrophyceae)

Chlorophyceae

Ulvophyceae

text: A newer proposed classification follows Leliaert et al. 2011[43] and modified with Silar 2016[44] for the green algae clades and Novíkov & Barabaš-Krasni 2015[45] for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.

text:
Chlorophyta

 ?Palmophyllales Zechman et al. 2010

 Prasinophyceae Christensen 1962 s.s.

 Nephroselmidophyceae Cavalier-Smith 1993

 Pseudoscourfieldiales Melkonian 1990 [Pycnococcales]

 Mamiellophyceae Marin & Melkonian 2010

 Pyramimonadophyceae

 Picocystis Lewin 2001

Tetraphytina

 ?Scourfieldiales Moestrup 1991

 Pedinophyceae Moestrup 1991

Chlorophytina

 Chlorodendrophyceae Massjuk 2006

 Trebouxiophyceae Friedl 1995

 Ulvophyceae Mattox & Stewart 1984

 Chlorophyceae Christensen 1994

Streptophyta s.l.

 ?Chlorokybophyta

 Mesostigmatophyta

 Klebsormidiophyta

Phragmoplastophyta

 Charophyta Rabenhorst 1863 emend. Lewis & McCourt 2004 (Stoneworts)

 Chaetosphaeridiales Marin & Melkonian 1999

 Coleochaetophyta

 Zygnematophyta

Embryophyta

 Marchantiophyta (Liverworts)

Stomatophyta

 Bryophyta (True mosses)

 Anthocerotophyta (Non-flowering hornworts)

Polysporangiophyta

 Horneophyta

 Lyonophyta

 Tracheophyta (Vascular Plants)

Green algae

text: Embryophytes

text: The plants that are likely most familiar to us are the multicellular land plants, called embryophytes. Embryophytes include the vascular plants, such as ferns, conifers and flowering plants. They also include the bryophytes, of which mosses and liverworts are the most common.

text: All of these plants have eukaryotic cells with cell walls composed of cellulose, and most obtain their energy through photosynthesis, using light, water and carbon dioxide to synthesize food. About three hundred plant species do not photosynthesize but are parasites on other species of photosynthetic plants. Embryophytes are distinguished from green algae, which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.

text: Bryophytes first appeared during the early Paleozoic. They can only survive where moisture is available for significant periods, although some species are desiccation-tolerant. Most species of bryophytes remain small throughout their life-cycle. This involves an alternation between two generations: a haploid stage, called the gametophyte, and a diploid stage, called the sporophyte. In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The bryophytes have the ability to secrete a cuticle on their outer surface, a waxy layer that confers resistant to desiccation. In the mosses and hornworts a cuticle is usually only produced on the sporophyte. Stomata are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange while controlling water loss.

text: Vascular plants first appeared during the Silurian period, and by the Devonian had diversified and spread into many different terrestrial environments. They developed a number of adaptations that allowed them to spread into increasingly more arid places, notably the vascular tissues xylem and phloem, that transport water and food throughout the organism. Root systems capable of obtaining soil water and nutrients also evolved during the Devonian. In modern vascular plants, the sporophyte is typically large, branched, nutritionally independent and long-lived, but there is increasing evidence that Paleozoic gametophytes were just as complex as the sporophytes. The gametophytes of all vascular plant groups evolved to become reduced in size and prominence in the life cycle.

text: The first seed plants, Pteridosperms (seed ferns), now extinct, appeared in the Devonian and diversified through the Carboniferous. In these the microgametophyte is reduced to pollen and the megagametophyte remains inside the megasporangium, attached to the parent plant. A megasporangium invested in protective layer called an integument is known as an ovule. After fertilisation by means of sperm deposited by pollen grains, an embryo develops inside the ovule. The integument becomes a seed coat, and the ovule develops into a seed. Seed plants can survive and reproduce in extremely arid conditions, because they are not dependent on free water for the movement of sperm, or the development of free living gametophytes.

text: Early seed plants are gymnosperms, as the ovules and subsequent seeds are not enclosed in a protective structure (carpels or fruit), but are found naked, typically on cone scales. Pollen typically lands directly on the ovule. Four surviving groups remain widespread now, particularly the conifers, which are dominant trees in several biomes.

text: Fossils

text: Plant fossils include roots, wood, leaves, seeds, fruit, pollen, spores, phytoliths, and amber (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. Pollen, spores and algae (dinoflagellates and acritarchs) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.

text: The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the Cambrian. These fossils resemble calcified multicellular members of the Dasycladales. Earlier Precambrian fossils are known that resemble single-cell green algae, but definitive identity with that group of algae is uncertain.

text: The oldest known fossils of embryophytes date from the Ordovician, though such fossils are fragmentary. By the Silurian, fossils of whole plants are preserved, including the lycophyte Baragwanathia longifolia. From the Devonian, detailed fossils of rhyniophytes have been found. Early fossils of these ancient plants show the individual cells within the plant tissue. The Devonian period also saw the evolution of what many believe to be the first modern tree, Archaeopteris. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds.

text: The Coal measures are a major source of Paleozoic plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; coal itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the Fossil Grove at Victoria Park in Glasgow, Scotland, the stumps of Lepidodendron trees are found in their original growth positions.

text: The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the Mesozoic and Cenozoic eras. Sequoia and its allies, magnolia, oak, and palms are often found.

text: Petrified wood is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by erosion. Petrified wood is often heavily silicified (the organic material replaced by silicon dioxide), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using lapidary equipment. Fossil forests of petrified wood have been found in all continents.

text: Fossils of seed ferns such as Glossopteris are widely distributed throughout several continents of the Southern Hemisphere, a fact that gave support to Alfred Wegener's early ideas regarding Continental drift theory.

text: The earliest fossils attributed to green algae date from the Precambrian (ca. 1200 mya).[46][47] The resistant outer walls of prasinophyte cysts (known as phycomata) are well preserved in fossil deposits of the Paleozoic (ca. 250-540 mya). A filamentous fossil (Proterocladus) from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the Cladophorales, while the oldest reliable records of the Bryopsidales, Dasycladales) and stoneworts are from the Paleozoic.[42][48]

text: Structure, growth and development

text: Most of the solid material in a plant is taken from the atmosphere. Through a process known as photosynthesis, most plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars. Parasitic plants, on the other hand, use the resources of their host to grow. These sugars are then used as building blocks and form the main structural component of the plant. Chlorophyll, a green-colored, magnesium-containing pigment is essential to this process; it is generally present in plant leaves, and often in other plant parts as well.

text: Plants usually rely on soil primarily for support and water (in quantitative terms), but also obtain compounds of nitrogen, phosphorus, potassium, magnesium and other elemental nutrients. Epiphytic and lithophytic plants depend on air and nearby debris for nutrients, and carnivorous plants supplement their nutrient requirements with insect prey that they capture. For the majority of plants to grow successfully they also require oxygen in the atmosphere and around their roots (soil gas) for respiration. Plants use oxygen and glucose (which may be produced from stored starch) to provide energy.[49] Some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as mangroves, can grow with their roots in anoxic conditions.

text: Factors affecting growth

text: The genotype of a plant affects its growth. For example, selected varieties of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.[50]

text: Growth is also determined by environmental factors, such as temperature, available water, available light, carbon dioxide and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth.

text: Biotic factors are also capable of affecting plant growth. Plants compete with other plants for space, water, light and nutrients. Plants can be so crowded that no single individual produces normal growth, causing etiolation and chlorosis. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of mycorrhizal fungi, and attacks by insects or plant diseases, including those caused by bacteria, fungi, viruses, and nematodes.[50]

text: Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other plants may be organized according to their seasonal growth pattern: annual plants live and reproduce within one growing season, biennial plants live for two growing seasons and usually reproduce in second year, and perennial plants live for many growing seasons and continue to reproduce once they are mature. These designations often depend on climate and other environmental factors; plants that are annual in alpine or temperate regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both evergreens that keep their leaves the entire year, and deciduous plants that lose their leaves for some part of it. In temperate and boreal climates, they generally lose their leaves during the winter; many tropical plants lose their leaves during the dry season.

text: The growth rate of plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025-0.250 mm/h. Some climbing species, such as kudzu, which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.

text: Plants protect themselves from frost and dehydration stress with antifreeze proteins, heat-shock proteins and sugars (sucrose is common). LEA (Late Embryogenesis Abundant) protein expression is induced by stresses and protects other proteins from aggregation as a result of desiccation and freezing.[51]

text: Effects of freezing

text: When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs within cells (intracellularly) or outside cells in intercellular spaces (Glerum 1985).[52] Intracellular freezing, which usually kills the cell (Lyons et al. 1979)[53] regardless of the hardiness of the plant and its tissues, seldom occurs in nature because rates of cooling are rarely high enough to support it. Rates of cooling of several degrees Celsius per minute are typically needed to cause intracellular formation of ice (Mazur 1977).[54]

text: At rates of cooling of a few degrees Celsius per hour, segregation of ice occurs in intercellular spaces, the “extraorgan ice” of Sakai and Larcher (1987)[55] and their coworkers. This may or may not be lethal, depending on the hardiness of the tissue.

text: The process of intercellular ice formation was described by Glerum (1985).[52] At freezing temperatures, water in the intercellular spaces of plant tissue freezes first, though the water may remain unfrozen until temperatures drop below −7 °C (19 °F). After the initial formation of ice intercellularly, the cells shrink as water is lost to the segregated ice, and the cells undergo freeze-drying. This dehydration is now considered the fundamental cause of freezing injury.

text: DNA damage and repair

text: Plants are continuously exposed to a range of biotic and abiotic stresses. These stresses often cause DNA damage directly, or indirectly via the generation of reactive oxygen species.[56] Plants are capable of a DNA damage response that is a critical mechanism for maintaining genome stability.[57] The DNA damage response is particularly important during seed germination, since seed quality tends to deteriorate with age in association with DNA damage accumulation.[58] During germination repair processes are activated to deal with this accumulated DNA damage.[59] In particular, single- and double-strand breaks in DNA can be repaired.[60] The DNA checkpoint kinase ATM has a key role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.[61]

text: Plant cells

text: Plant cells are typically distinguished by their large water-filled central vacuole, chloroplasts, and rigid cell walls that are made up of cellulose, hemicellulose, and pectin. Cell division is also characterized by the development of a phragmoplast for the construction of a cell plate in the late stages of cytokinesis. Just as in animals, plant cells differentiate and develop into multiple cell types. Totipotent meristematic cells can differentiate into vascular, storage, protective (e.g. epidermal layer), or reproductive tissues, with more primitive plants lacking some tissue types.[62]

text: Physiology

text: Photosynthesis

text: Plants are photosynthetic, which means that they manufacture their own food molecules using energy obtained from light. The primary mechanism plants have for capturing light energy is the pigment chlorophyll. All green plants contain two forms of chlorophyll, chlorophyll a and chlorophyll b. The latter of these pigments is not found in red or brown algae. The simple equation of photosynthesis is as follows:-

text: 6CO2 + 6H2O → (in the presence of light and chlorophyll) C6H12O6 + 6O2

text: Immune system

text: By means of cells that behave like nerves, plants receive and distribute within their systems information about incident light intensity and quality. Incident light that stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a bundle sheath cell. Researchers, from the Warsaw University of Life Sciences in Poland, found that plants have a specific memory for varying light conditions, which prepares their immune systems against seasonal pathogens.[63] Plants use pattern-recognition receptors to recognize conserved microbial signatures. This recognition triggers an immune response. The first plant receptors of conserved microbial signatures were identified in rice (XA21, 1995)[64] and in Arabidopsis thaliana (FLS2, 2000).[65] Plants also carry immune receptors that recognize highly variable pathogen effectors. These include the NBS-LRR class of proteins.

text: Internal distribution

text: Vascular plants differ from other plants in that nutrients are transported between their different parts through specialized structures, called xylem and phloem. They also have roots for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.[62]

text: Genomics

text: Plants have some of the largest genomes among all organisms.[66] The largest plant genome (in terms of gene number) is that of wheat (Triticum asestivum), predicted to encode ~94,000 genes[67] and thus almost 5 times as many as the human genome. The first plant genome sequenced was that of Arabidopsis thaliana which encodes about 25,500 genes.[68] In terms of sheer DNA sequence, the smallest published genome is that of the carnivorous bladderwort (Utricularia gibba) at 82 Mb (although it still encodes 28,500 genes)[69] while the largest, from the Norway Spruce (Picea abies), extends over 19,600 Mb (encoding about 28,300 genes).[70]

text: Ecology

text: The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis radically changed the composition of the early Earth's atmosphere, which as a result is now 21% oxygen. Animals and most other organisms are aerobic, relying on oxygen; those that do not are confined to relatively rare anaerobic environments. Plants are the primary producers in most terrestrial ecosystems and form the basis of the food web in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.

text: Land plants are key components of the water cycle and several other biogeochemical cycles. Some plants have coevolved with nitrogen fixing bacteria, making plants an important part of the nitrogen cycle. Plant roots play an essential role in soil development and prevention of soil erosion.

text: Distribution

text: This section needs expansion. You can help by adding to it. (June 2008)

text: Plants are distributed worldwide in varying numbers. While they inhabit a multitude of biomes and ecoregions, few can be found beyond the tundras at the northernmost regions of continental shelves. At the southern extremes, plants have adapted tenaciously to the prevailing conditions. (See Antarctic flora.)

text: Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's biomes are named for the type of vegetation because plants are the dominant organisms in those biomes, such as grasslands and forests.

text: Ecological relationships

text: Numerous animals have coevolved with plants. Many animals pollinate flowers in exchange for food in the form of pollen or nectar. Many animals disperse seeds, often by eating fruit and passing the seeds in their feces. Myrmecophytes are plants that have coevolved with ants. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from herbivores and sometimes competing plants. Ant wastes provide organic fertilizer.

text: The majority of plant species have various kinds of fungi associated with their root systems in a kind of mutualistic symbiosis known as mycorrhiza. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for endophytic fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, Neotyphodium coenophialum, in tall fescue (Festuca arundinacea) does tremendous economic damage to the cattle industry in the U.S.

text: Various forms of parasitism are also fairly common among plants, from the semi-parasitic mistletoe that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic broomrape and toothwort that acquire all their nutrients through connections to the roots of other plants, and so have no chlorophyll. Some plants, known as myco-heterotrophs, parasitize mycorrhizal fungi, and hence act as epiparasites on other plants.

text: Many plants are epiphytes, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. Hemiepiphytes like the strangler fig begin as epiphytes but eventually set their own roots and overpower and kill their host. Many orchids, bromeliads, ferns and mosses often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata that may contain complex aquatic food webs.[71]

text: Approximately 630 plants are carnivorous, such as the Venus Flytrap (Dionaea muscipula) and sundew (Drosera species). They trap small animals and digest them to obtain mineral nutrients, especially nitrogen and phosphorus.[72]

text: Importance

text: This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (June 2016) (Learn how and when to remove this template message)

text: The study of plant uses by people is termed economic botany or ethnobotany;[73] some consider economic botany to focus on modern cultivated plants, while ethnobotany focuses on indigenous plants cultivated and used by native peoples.[citation needed] Human cultivation of plants is part of agriculture, which is the basis of human civilization.[74] Plant agriculture is subdivided into agronomy, horticulture and forestry.[75]

text: Foods and beverages

text: Much of human nutrition depends on plants, either directly through foods and beverages consumed by people, or indirectly as feed for animals or the flavoring of foods. The science of agriculture deals with the planting, raising, nutrition, and harvest of food crops, and has played a key role in the history of world civilizations.

text: Human nutrition depends to a large extent on cereals, especially maize (or corn), wheat, rice, oats, and millet. Large areas of many countries are given over to the cultivation of cereals for local consumption or export to other countries. Livestock animals including cows, pigs, sheep, goats and camels are all herbivores; and most feed primarily or entirely on cereal plants. Cereals are staple crops, meaning that they provide calories (in the form of complex carbohydrates such as starch) that are needed to fuel daily activities, and thus form the foundation of a daily diet. Other staple crops include potatoes, cassava, yams, and legumes.

text: Human food also includes vegetables, which consist principally of leaves and stems eaten as food. Vegetables are important for the vitamins, minerals, and dietary fiber they supply. Fruits provide a higher quantity of sugars and have a sweeter taste than vegetables. However, whether a particular food is considered a "vegetable" or a "fruit" will depend on context, since the word fruit has a more precise definition in botany than it does in general use. Nuts and seeds, including foods such as peanuts, walnuts, almonds, and pistachios, contain unsaturated fats that are also necessary for a healthy diet. As with fruits, the terms nut and seed have stricter definitions in plant science.

text: Many plants are used to flavor foods. Such plants include herbs (e.g. rosemary and mint), which come from the green leafy parts of plants, and spices (e.g. cumin and cinnamon), which come from other plant parts. Some plants produce edible flowers, which may be added to salads or used to decorate foods. Sweeteners such as sugar and stevia are derived from plants. Sugar is obtained mainly from sugar cane and sugar beet, and honey is created when bees regurgitate the nectar from flowers. Cooking oils and margarine come from maize, soybean, rapeseed, safflower, sunflower, olive and others. Food additives include gum arabic, guar gum, locust bean gum, starch and pectin.

text: Plants are also the source of beverages produced either by infusion, such as coffee and tea; by fermentation, such as beer and wine; or by distillation, such as whisky, vodka, rum, and other alcoholic spirits.

text: Nonfood products

text: Plants are the source of many natural products such as essential oils, natural dyes, pigments, waxes, resins, tannins, alkaloids, amber and cork. Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber, latex, lubricants, linoleum, plastics, inks, and gums. Renewable fuels from plants include firewood, peat and many other biofuels. Coal and petroleum are fossil fuels derived from the remains of plants. Olive oil has been used in lamps for centuries to provide illumination.

text: Structural resources and fibers from plants are used in both the construction of dwellings and the manufacture of clothing. Wood is used not only for buildings, boats, and furniture, but also for smaller items such as musical instruments and sports equipment. Wood also may be pulped for the manufacture of paper and cardboard. Cloth is often made from cotton, flax, ramie or synthetic fibers derived from cellulose, such as rayon and acetate. The thread that is used to sew cloth likewise comes from plant fibers. Hemp and jute are grown for their fibers, which may be woven into rope or rough sacking.

text: Plants are also a primary source of basic chemicals, both for their medicinal and physiological effects, as well as for the industrial synthesis of a vast array of organic chemicals. Medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. There are hundreds of herbal supplements such as ginkgo, Echinacea, feverfew, and Saint John's wort. Pesticides derived from plants include nicotine, rotenone, strychnine and pyrethrins. Certain plants contain psychotropic chemicals that are extracted and ingested, including tobacco, cannabis (marijuana), opium, and cocaine. Poisons from plants include ricin, hemlock and curare.

text: Aesthetic uses

text: Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to historic gardens, national parks, rainforests, forests with colorful autumn leaves, and the National Cherry Blossom Festival.

text: While some gardens are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. Arboretums and botanical gardens are public collections of living plants. In private outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Gardens may cultivate the plants in a naturalistic state, or may sculpture their growth, as with topiary or espalier. Gardening is the most popular leisure activity in the U.S., and working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities.

text: Plants may also be grown or kept indoors as houseplants, or in specialized buildings such as greenhouses that are designed for the care and cultivation of living plants. Venus Flytrap, sensitive plant and resurrection plant are examples of plants sold as novelties. There are also art forms specializing in the arrangement of cut or living plant, such as bonsai, ikebana, and the arrangement of cut or dried flowers. Ornamental plants have sometimes changed the course of history, as in tulipomania.

text: Architectural designs resembling plants appear in the capitals of ancient Egyptian columns, which were carved to resemble either the Egyptian white lotus or the papyrus. Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.

text: Scientific and cultural uses

text: Basic biological research has often been done with plants. In genetics, the breeding of pea plants allowed Gregor Mendel to derive the basic laws governing inheritance, and examination of chromosomes in maize allowed Barbara McClintock to demonstrate their connection to inherited traits. The plant Arabidopsis thaliana is used in laboratories as a model organism to understand how genes control the growth and development of plant structures. Space stations or space colonies may one day rely on plants for life support.

text: Ancient trees are revered and many are famous. Tree rings themselves are an important method of dating in archeology, and serve as a record of past climates.

text: Plants figure prominently in mythology, religion and literature. They are used as national and state emblems, including state trees and state flowers. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. The arrangement of flowers may be used to send hidden messages.

text: The field of ethnobotany studies plant use by indigenous cultures, which helps to conserve endangered species as well as discover new medicinal plants.

text: Negative effects

text: Weeds are uncultivated and usually unwanted plants growing in managed environments such as farms, urban areas, gardens, lawns, and parks. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species. Invasive plants cause costly damage in crop losses annually by displacing crop plants, they further increase the cost of production and the use of chemicals to control them, which in turn affects the environment.

text: Plants may cause harm to animals, including people. Plants that produce windblown pollen invoke allergic reactions in people who suffer from hay fever. A wide variety of plants are poisonous. Toxalbumins are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including tobacco, cannabis (marijuana), cocaine and opium. Smoking causes damage to health or even death, while some drugs may also be harmful or fatal to people.[76][77] Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.[78][79] Some plants cause allergic reactions when ingested, while other plants cause food intolerances that negatively affect health.


document_title: Veronica Mars (season 3)

question_text: when do veronica and logan break up in season 3

text: Veronica Mars (season 3)

text: Cast[edit]

text: The third season features a cast of ten actors who receive billing,[2] an increase from the nine actors in the second.[3] Kristen Bell portrays the titular Veronica Mars, a college student and skilled private detective. Jason Dohring plays Logan Echolls, Veronica's love interest. Ryan Hansen plays Logan's obnoxious friend Dick Casablancas. Percy Daggs III portrays Wallace Fennel, Veronica's best friend and frequent partner in solving mysteries. Francis Capra portrays Eli "Weevil" Navarro, the previous leader of the Pacific Coast Highway (PCH) biker gang and Veronica's friend. Enrico Colantoni plays Veronica's father Keith Mars, a private investigator and former Balboa County Sheriff.

text: Cindy "Mac" Mackenzie and Don Lamb, recurring characters in the first two seasons, were upgraded to series regulars in the third. Mac, portrayed by Tina Majorino, was a computer expert befriended by Veronica. Lamb, portrayed by Michael Muhney, was the Balboa County Sheriff who won the office from Keith in the recall election.[4] The third season introduces two new series regulars, Julie Gonzalo portrays Parker Lee and Chris Lowell plays Stosh "Piz" Piznarski.[4] Piz, named after the director of the pilot, Mark Piznarski, was created so that Veronica could have a male friend of middle-class status rather than of upper-class. He is Wallace's roommate and a friend of Veronica, and his campus radio show serves as a narrative device to capture the mood of the university.[5] Parker is Mac's extroverted roommate at Hearst College and "everything that [she] is not", according to Thomas.[4]

text: Regular characters who did not return for the third season were Duncan Kane (played by Teddy Dunn), who left the country with his daughter midway through the second season, Jackie Cook (Tessa Thompson), who returned to New York, and Cassidy Casablancas (Kyle Gallner), who committed suicide in the season two finale.

text: Release[edit]

text: Critical reception[edit]

text: Reviews of the third season were mixed compared to the previous two seasons. Maureen Ryan of the Chicago Tribune praised Bell's performance, who she said deserved the "truckload of glowing press notices for her work as the tightly wound, emotionally resilient young detective". Ryan thought Veronica's relationship with Keith was "one of the best, if not the best, parent-child relationship on television", and described Logan and Veronica's on-screen chemistry as "sizzling".[6] Stephanie Zacharek of Salon.com felt that although the third season "wasn't the strongest", it did show that Veronica Mars "could not only survive but continue to find ways to reinvigorate itself". Zacharek liked newcomer Piz, and realized how much she was going to miss the character Dick.[7] Melanie McFarland of the Seattle Post-Intelligencer felt that Veronica Mars "easily has a few more seasons left in it", and described the writing as "unfailingly hysterical and clever". McFarland praised the cast as "without a doubt one of the most likable on television", and called Dohring "the most beloved of the bunch".[8]

text: Keith McDuffee of TV Squad deemed the season "disappointing", mainly because the episodes offered nothing new: "most fans of Veronica Mars felt that season three was clearly its weakest".[9] Eric Goldman of IGN said that the main issue was the shift in the overall tone, with a lighter feeling than the previous seasons. Goldman believed that Logan had been most affected by the tone change; he was robbed of his darker aspects and changed into an "increasingly extraneous character". The reviewer felt that despite the concerns over the final five episodes, the series ended with "three very strong episodes, with lots of strong dialogue". Goldman concluded that although third season "was very choppy", it still had "plenty of witty dialogue and a continually engaging performance by Kristen Bell as the title character".[10] The Pittsburgh Post-Gazette opined that Veronica Mars had taken a dive "creatively", from "the mopier version of its theme song to stalled storylines". The reviewer felt that "the arcing mysteries had grown less convincing and compelling as time went on and were too drawn out".[11] Fox News Channel's Bridget Byrne pointed out that Veronica had "gone from punky to—dare we say—preppy" in the third season.[12]

text: Ratings and awards[edit]

text: The third-season premiere was watched by 3.36 million American viewers, an increase from the 2.42 million viewers who viewed the second-season finale.[13][14] Ratings remained stable for the first ten episodes, and the ninth episode featured the most viewers of the season with 3.44 million.[15] Beginning with the eleventh episode, ratings dropped to a consistent viewership of a mid-2 million per episode,[16] and the final episode before the hiatus was watched by 2.66 million viewers.[17] When the series returned from its hiatus, viewers had decreased to 2.35 million,[18] and the final two episodes garnered only 1.78 and 2.15 million viewers respectively.[19]

text: The third season averaged 2.5 million viewers for all 20 episodes. Out of all regular primetime programming that aired during the 2006–2007 American television season, Veronica Mars ranked 138th out of 142, according to the Nielsen ratings system.[20] The third season was nominated for two awards: Kristen Bell was nominated for the Saturn Award for Best Actress on Television,[21] and the series was nominated for the Writers Guild of America Award for On-Air Promotion (Radio or Television).[22]

text: Distribution[edit]

text: The first two seasons of Veronica Mars aired on UPN; however, in 2006, CBS Corporation and Warner Bros. decided to merge UPN and The WB into The CW. Paul Maguire, the spokesman for The CW, said that the series was picked up because "the critics are behind it and our research has consistently shown that Gilmore shared more audience commonality with Veronica than with any other show from UPN, except Top Model".[23]

text: The third season was released in the US under the title Veronica Mars: The Complete Third Season as a widescreen six-disc Region 1 DVD box set on October 23, 2007,[24] Region 2 on December 12, 2008,[25] and Region 4 on February 11, 2009.[26] In addition to all of the aired episodes, DVD extras included unaired scenes with introductions by Rob Thomas, a gag reel, and a webisode gallery with cast interviews and various set tours. Also included were the featurettes, "Going Undercover with Rob Thomas" commentary and "Pitching Season 4", an interview with Thomas discussing a new direction for the series that picks up years later, with Veronica as a rookie FBI agent.[27]

text: The third season was simulcast in Canada by Fox 44.[28] The series had previously been broadcast in Canada by the CTV Television Network and Sun TV.[29][30] Despite airing the series to low ratings in the previous seasons, the United Kingdom's Living decided to air the series' third season.[31] Network Ten began airing the third season in Australia on March 30, 2007.[32] The series went on hiatus after the fourth episode on April 20, 2007,[33] and resumed on the newly created Ten HD in 2008.[34] The finale was aired on April 8, 2008.[35] The third season was broadcast in New Zealand by TV2.[36]

text: Cancellation and future[edit]

text: At the 2007 CW Upfront, Ostroff announced that Veronica Mars was not part of the new primetime lineup and was "not coming back".[37] When asked if the series could continue with the FBI concept, Ostroff said that the series was completely gone "in any form".[38] Upon the cancellation of the series, a group of fans calling themselves the "Cloud Watchers" sent more than 10,000 Mars bars to the CW,[39] hoping that the network would reverse its decision and renew the series.[40]

text: Thomas stated that he was interested in writing a feature film based on the series, in the interest of providing closure to the storylines and character arcs. In September 2008, Thomas told Entertainment Weekly that "I thought I had the idea broken, but I've hit a wall in the final act that I haven't quite figured out". Thomas explained that he was very busy writing for Cupid and Party Down, both of which he created.[41] In January 2009, TV Guide reported that the film was Thomas' first priority after Cupid. Thomas noted that as well as writing the script, someone would need to pay for the film, but indicated that producer Joel Silver was ready to green-light the film.[42] In late March, Thomas stated that although the film was not green-lit by the studio, the possibility was still there. Thomas revealed that the film would take place before Veronica's graduation, and feature Wallace, Logan, Mac and Weevil.[43]

text: A film continuation, released in early 2014, was confirmed after a successful Kickstarter campaign launched by Rob Thomas which raised over $5.7 million.[44]

text: Episodes[edit]

text: Veronica is still living at home with her father Keith, and Piz and Parker are introduced as the respective roommates of Veronica's friends Wallace and Mac. Weevil takes a job at Hearst as a maintenance man, while Lamb continues to serve as Sheriff. During the season, Keith begins an affair with a married client, Wallace struggles to balance academics and sports, Mac begins dating again after previous failed relationships, and Dick has a breakdown and appeals to Logan for help. The season chronicles Veronica and Logan's failing attempts to maintain their relationship in the face of Veronica's mistrust.

text:
No.
overall
No. in
season
Title
Directed by
Written by
Original air date
Prod.
code
U.S. viewers
(millions)

45
1
"Welcome Wagon"
John Kretchmer
Rob Thomas
October 3, 2006 (2006-10-03)
3T5801
3.36[14]

The fall term at Hearst College starts and Veronica and Logan are dating. Veronica is still living at home, and Mac and Wallace each have roommates. Wallace's roommate Piz asks Veronica to recover his stolen possessions. Veronica sneaks into Parker and Mac's darkened room to retrieve an item, and successfully avoids disturbing what she thinks is consensual sex. Parker later awakens from her drugged stupor to find her head shaved, and Veronica is horrified to realize she unintentionally allowed Parker to be raped.

46
2
"My Big Fat Greek Rush Week"
John Kretchmer
Diane Ruggiero
October 10, 2006 (2006-10-10)
3T5802
2.96[45]

Guilty over not having helped Parker, Veronica pursues the Hearst serial rapist by going undercover at the Theta Beta sorority during rush week. Parker's parents arrive, intending to take her home. Wallace and Logan participate in a guard/prisoner experiment for sociology class. On the night she was raped, Parker was taken back to her dorm room by a resident assistant because she was too intoxicated to get back herself. Veronica also learns that someone from Theta Beta could have had access to the keys to Parker's dorm room.

47
3
"Wichita Linebacker"
Harry Winer
Phil Klemmer & John Enbom
October 17, 2006 (2006-10-17)
3T5803
3.12[46]

To help Weevil stay out of prison, Veronica convinces her father to give him a job at Mars Investigations. A Hearst football player loses the team playbook and, with his scholarship at stake, hires Veronica to find it. Veronica fights with Logan after she discovers that he chose to gamble with his friends instead of spending time with her. The Dean of Hearst threatens to expel Veronica unless she reveals her sources for a sorority article she wrote. Claire, one of the girls of Lilith House, a center of feminist activism, is raped.

48
4
"Charlie Don't Surf"
Jason Bloom
Diane Ruggiero & Jason Elen
October 24, 2006 (2006-10-24)
3T5804
3.33[47]

Logan asks Veronica and Keith to discover why his trust fund money is disappearing. With a court hearing approaching, Dick and the Pi-Sigs hire Veronica to prove their innocence, to the chagrin of Parker and the other rape victims. Keith's friend Harmony hires him to prove her husband is cheating, and the two grow close. Veronica investigates Claire's rape, and learns that she was with a man the night that she was raped.

49
5
"President Evil"
Nick Marck
Jonathan Moskin & David Mulei
October 31, 2006 (2006-10-31)
3T5805
2.70[48]

Veronica attends Mercer's Halloween party at the campus casino, but before Logan arrives, the party is robbed by armed men wearing masks modeled after past United States presidents. Weevil is arrested for the crime, but Veronica suspects he has been framed when it is revealed that the loot was dumped and the guns were not real. Keith looks for the ex-husband of the Dean's wife as a possible bone marrow donor for her critically ill son. Veronica finds out that the man Claire was with the night of her rape is her boyfriend; however, she claims that she does not know him.

50
6
"Hi, Infidelity"
Michael Fields
John Enbom
November 7, 2006 (2006-11-07)
3T5806
2.75[49]

Veronica is accused of plagiarizing her criminology research paper. Seeking to clear herself, she discovers that Professor Landry is having an affair with Dean O'Dell's wife. Wallace is pardoned by the Dean for cheating on his exam, but resigns from the basketball team to focus on his studies. Piz invites Veronica to a night of bowling and she decides to bring Logan and Parker, unaware Piz wanted the evening to be more of a date. Veronica learns that the Lilith House rape was faked, and no hair or DNA from the rapist had been found at the crime scenes. Mercer is arrested after Parker recognizes his cologne to be the rapist's, and Veronica finds clippers in his room.

51
7
"Of Vice and Men"
Harry Winer
Phil Klemmer
November 14, 2006 (2006-11-14)
3T5807
2.69[50]

Increasingly frustrated by what she sees as dishonesty by Keith, Logan, and Professor Landry, Veronica withdraws from all of them. While staying at Wallace and Piz's dorm room, she meets a girl trying to locate her missing boyfriend. Professor Landry offers Veronica an internship with the FBI, Keith breaks up with Harmony after being blackmailed by Vinnie Van Lowe, and Mercer is cleared of being the rapist by providing an alibi. After being drugged at the food court, Veronica almost becomes the rapist's latest victim, but he is frightened off by Logan arriving at the scene at the last minute.

52
8
"Lord of the Pi's"
Steve Gomer
Diane Ruggiero
November 21, 2006 (2006-11-21)
3T5808
2.57[51]

Keith and Veronica are hired to find the missing granddaughter of the founder of Hearst College. They learn that the granddaughter's swing vote could spell the end of fraternities and sororities at Hearst. Logan fears for Veronica's safety as she continues to investigate the campus rapes. The girls at Lilith House explain that they faked Claire's rape to help shut down the Greek houses on campus, which they believed were responsible for the real rapes. Patty Hearst guest stars as a Hearst College trustee called "Selma Hearst Rose".

53
9
"Spit & Eggs"
Rob Thomas
Rob Thomas
November 28, 2006 (2006-11-28)
3T5809
3.44[15]

Logan offers Veronica a choice, but neither option is beneficial for their relationship. To salvage their friendship, Logan dumps Veronica as a girlfriend. Under pressure, Dean O'Dell reinstates the Greek system. Veronica discovers the identity of the Hearst rapist after a Pi Sig fraternity party, but also finds herself in trouble. Keith tells Dean O'Dell about his wife's affair, and Weevil finds him dead hours later from a gunshot wound. Logan attacks a police car to get arrested and exact vengeance on the rapist for attacking Veronica.

54
10
"Show Me the Monkey"
Nick Marck
Story by: John Enbom
Teleplay by: John Enbom & Robert Hull
January 23, 2007 (2007-01-23)
3T5810
3.23[52]

Six weeks later, Dean O'Dell's death has been ruled a suicide. Mindy O'Dell asks Keith to investigate the Dean's death because his insurance policy does not cover suicide. Mac and Veronica go undercover as animal rights activists to find a missing lab monkey. Veronica talks to Piz about not letting things slip by, not realizing that he is trying to ask her out. Logan is upset after breaking up with Veronica and she realises that she wants Logan back in her life and shows up at his door and the pair decide to get back together.

55
11
"Poughkeepsie, Tramps and Thieves"
John Kretchmer
Diane Ruggiero
January 30, 2007 (2007-01-30)
3T5811
2.69[16]

A classmate asks Veronica to locate the woman he loves; she is later revealed to be a hooker. Keith continues his investigation of Dean O'Dell's murder by visiting the Lilith House girls. Veronica asks Logan some difficult relationship questions, and learns he had sex with someone else while they were split up but accepts it. Keith learns that three of the Lilith House girls were in the area of the Dean's office around the time of his murder, which was egged by unknown assailants.

56
12
"There's Got to Be a Morning After Pill"
Tricia Brock
Story by: Jonathan Moskin & David Mulei
Teleplay by: Jonathan Moskin & Phil Klemmer & John Enbom
February 6, 2007 (2007-02-06)
3T5812
2.40[53]

A student asks Veronica to find out who slipped her RU-486, which caused a miscarriage. While searching through Tim Foyle's computer, Veronica discovers that he is also investigating Dean O'Dell's murder, which took place at around 2:20 am. Upon learning that Logan slept with Madison Sinclair after their first break up, Veronica breaks up with him. Keith discovers that Mindy's car was egged on the night of the Dean's murder, which suggests that she was lying about her whereabouts at the time.

57
13
"Postgame Mortem"
John Kretchmer
Joe Voci
February 13, 2007 (2007-02-13)
3T5813
2.37[54]

Logan is upset after Veronica breaks up with him, so Dick invites two girls over to cheer him up, but Logan has to babysit an eleven-year-old girl instead. Keith and Veronica discover that the alibis given by Mindy O'Dell and Professor Landry do not match. Wallace rejoins the Hearst basketball team right before the coach is found dead. His widow hires Keith to investigate the murder and clear her son Josh. When Josh escapes from prison, Veronica is arrested for allegedly being his accomplice.

58
14
"Mars, Bars"
Harry Winer
Story by: Phil Klemmer & John Enbom & Joe Voci
Teleplay by: Phil Klemmer & John Enbom
February 20, 2007 (2007-02-20)
3T5814
2.27[55]

Without any evidence to hold her, Sheriff Lamb releases Veronica from jail. Keith learns that the coach's wife hired Vinnie Van Lowe to find out if her husband was having an affair, while Josh makes contact with Veronica and insists that he is being framed for his father's murder. Logan joins Mac and Parker on a Valentine's Day scavenger hunt, and draws closer to Parker. Lamb attempts to apprehend a suspect without waiting for backup, and is killed.

59
15
"Papa's Cabin"
Michael Fields
John Enbom
February 27, 2007 (2007-02-27)
3T5815
2.66[17]

Keith, again appointed sheriff after Lamb's death, interrogates Mindy O'Dell, who reveals that the third man in her hotel room the night of the Dean's murder was Dean O'Dell himself. Veronica and Tim set out to prove Professor Landry's innocence, and Veronica ends up uncovering the real murderer.

60
16
"Un-American Graffiti"
John Kretchmer
Robert Hull
May 1, 2007 (2007-05-01)
3T5816
2.35[18]

Veronica is hired by a Middle Eastern restaurant owner to find out who has been vandalizing his family business. When a drunken teenager stumbles from a bar and gets hit by a car, Keith orders his deputies to conduct surprise ID checks. While doing his own surprise search, Keith catches Piz and Wallace using fake ID's provided by Veronica. Logan decides to throw a birthday party for Parker, where Veronica and Piz kiss.

61
17
"Debasement Tapes"
Dan Etheridge
John Enbom
May 8, 2007 (2007-05-08)
3T5817
1.85[56]

Piz escorts aging rock star Desmond Fellows (Paul Rudd guest stars) before a benefit concert for the radio station. When Fellows' irreplaceable backing tapes go missing, Piz recruits Veronica to locate them. Vinnie Van Lowe files to oppose Keith in the special election for sheriff.

62
18
"I Know What You'll Do Next Summer"
Nick Marck
Jonathan Moskin & David Mulei
May 15, 2007 (2007-05-15)
3T5818
2.10[57]

Veronica passes the Private Investigator license exam, while Piz interviews Apollo Bukenya, an African student at Hearst who wrote a book about his years as an orphan child-soldier. Veronica is hired by an African man to help prove that he is Apollo's father, but her investigation risks exposing Apollo as a fraud. Meanwhile, as the election nears, Keith fights a crime spree in Neptune. Parker consults Veronica for advice about Logan.

63
19
"Weevils Wobble But They Don't Go Down"
Jason Bloom
Phil Klemmer
May 22, 2007 (2007-05-22)
3T5819
1.78[19]

Weevil is arrested for selling fake debit cards, but claims he is being framed and asks Veronica for help. On Piz's radio show, Keith debates Vinnie Van Lowe about the upcoming election, while Dick drunkenly apologizes to Mac for the way he has treated her. Veronica and Piz make up after their argument, and a sex tape of them is posted on the internet. Dick shows the sex tape to Logan who thinks Piz filmed the act without Veronica's knowledge and beats him up at his radio show.

64
20
"The Bitch Is Back"
Michael Fields
Rob Thomas & Diane Ruggiero
May 22, 2007 (2007-05-22)
3T5820
2.15[19]

Angry that Logan attacked Piz, Veronica tells him to leave her alone. Parker confronts Logan about his continuing feelings for Veronica and breaks up with him, while Piz assures Veronica that he had nothing to do with the sex video. Veronica, with Weevil's help, investigates how the tape originated and discovers Jake Kane is linked to The Castle and pays him a visit. Logan apologises to Veronica for attacking Piz and beats up the real culprit in the cafeteria after which he apologises to Piz.