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there's a good chance you know the cats
and dogs on your block better than you
know the trees and flowers and hey that
makes sense
no judgment here after all plants don't
greet you on the sidewalk getting fights
with raccoons or sneak up on you when
you're walking home in the dark they
keep a low profile but really plants are
amazing they give us food and oxygen
they decorate our homes and they're also
really fascinating organisms we've
talked about plants a ton on this
channel and thought it was about time to
compile some of our favorite episodes
about them speaking of time here's Hank
to explain how plants can tell what time
it is because you know apparently that's
something they can do
plants don't have brains it's probably
not news to anyone plants also don't
have muscles or anything resembling a
nervous system and yet they can move in
some plants this is actually pretty
dramatic think venus flytrap but there
are tons of plants that move more slowly
and they do it in time with the coming
of day and night so how do they move and
how do they know when to do it all
without a brain or any of that other
stuff many plants such as members of the
legume and wood sorrel families tuck
their leaves in at night we don't
totally understand how this happens and
we have almost no idea why but
scientists have identified some of the
players involved the process of how
plants tucked themselves in at night is
called Nick tenacity nastic movements
are a plant's movement in response to a
stimulus that doesn't occur in a
particular direction the leaves don't
follow the moon or anything they just
drew temperature change plays a role in
this response the cooler night air can
help signal the plant's reaction and the
warming Sun in the morning does the
opposite but it gets quite a bit more
sophisticated than that involving not
just temperature changes but several
different types of chemical reactions
one player in this process is a molecule
called a phytochrome which absorbs light
phytochrome participates in a reversible
chemical reaction meaning it doesn't
just react to form a product and then
stop instead it can switch back and
forth between two different forms
depending on the conditions these two
forms are called PR and PFR initially
phytochrome takes the form of PR
so-called because it absorbs red light
which there's more of during the day
when the Sun is out as PR absorbs red
light however it is converted into PFR
which absorbs far red light instead
basically the less intense wavelengths
as the Sun sets absorption of far red
light causes PFR to convert back to PR
some of it will change back over time in
the absence of any light as well which
means that the phytochrome automatically
cycles back and forth between forms
depending on whether it's day or night
these changing forms of phytochrome are
important in structures called pol vinay
appli- is a region of bulbous tissue at
the base of a leaf
that ax is a flexible joint it's like a
plant elbow when enough pfr is present
in the pulvinus the plant pumps water to
a specific section of the joint the
change in water pressure within the
cells called turgor pressure basically
flexes the joint like a muscle which
bundles the leaves up for the night when
the chemical reaction reverses the
turgor pressure shifts back additional
leaf chemicals called leaf closing and
leaf opening substances also play a part
in night time well leaf opening and
closing there's a lot of variety in
these chemicals but the general idea of
oscillating chemical reactions is
similar in the same way many flowers
open in the morning and close at night
for reasons that are even more poorly
understood it might be to conserve a
flower scent to protect their nectar to
keep all and dry some other reason but
the mechanism might be similar petals
after all are just a type of leaf this
isn't the only kind of day and night
plant movement either many species
actively follow the Sun during the day
in a process called heliotropism unlike
nastic movements tropisms our plant
movements that are oriented in a
specific direction heliotropism can help
leaves get the most possible sunlight
often heliotropism in leaves is also
controlled by turgor pressure in pull
vine I if you wanted a lot of new
terminology all in one sentence so in
this case the leaves can move
continuously to track the Sun throughout
the day rather than just opening and
closing and some flowers follow the Sun
too it seems to have a few benefits like
providing a nice warm place for
pollinators and helping the plants seeds
develop but many Helio tropic flowers
have no pull Vinay young sunflowers
instead turned to face the Sun by
growing their stem on one side at a time
it's not totally clear what chemicals
the sunflower is used to sense sunlight
but the changes in stem growth appear to
be governed by a hormone called auxin
which in this case tells certain parts
of the plant to grow in response to
light the stem of the sunflower grows
faster on the side that gets less light
thanks to a higher level of auxin
activity on the shady side that tilts
the developing flower toward the Sun at
night in the absence of sunlight
sunflower stems reorient themselves to
face east
and in the morning the light directed
growth process resumes but sunflower
stalks don't keep growing forever solar
tracking only happens in young
sunflowers once they're fully mature the
flowers face east and never move again
so now you know how to tell what
direction things are if you're in the
middle of a sunflower field and you also
know that plants don't need brains or
nervous systems or muscles to respond to
their environments as long as they've
got chemistry on their side and they're
more sophisticated about it than we
think able to keep track of time and act
appropriately which is pretty smart
so plants know when the Sun rises and
sets that means in my part of the world
they know that the Sun is starting to
set earlier and things are cooling down
around our office we've started keeping
the windows and doors shut to block out
the winter chill but if you're doing the
same thing at home things might start to
feel a bit stuffy so in place of that
fresh air wafting in with a breeze could
you just keep a few houseplants to
purify the air instead here's what the
science says
it seems like every workplace has that
one person who swears that the potted
spider-plant sitting on their desk has
an almost magical ability to purify the
air in the office are they actually onto
something there is evidence to show that
plants can remove pollutants from indoor
air but a single potted plant probably
won't go the distance if you've heard
that bringing plants into your home or
office will improve your indoor air
quality you probably have a study
conducted back in 1989 by NASA to thank
for that the goal was to test whether a
variety of types of indoor plants could
be used for air purification both on
earth and in space the plants were put
into sealed containers and the air
pumped full of chemicals including
benzene and formaldehyde those chemicals
fall under the broader umbrella of
volatile organic compounds or VOCs some
VOCs are known to cause health issues
like headaches or liver and kidney
damage and they're noteworthy as indoor
pollutants because household products
and building materials can give them off
the plants are kept under controlled
conditions with plenty of light and
water and the air quality was measured
over a 24-hour period the study found
the majority of plants included in the
experiment removed much of the benzene
and formaldehyde from the container
plants are thought to remove pollutants
from the surrounding air by absorbing
the gases through their leaves and roots
with some possible help from the
microorganisms in the soil so that's it
right house plans help clean the air
well not quite leader study is doing
similar experiments have yielded mixed
results a 2009 study tested 28 varieties
of indoor plants and found four that
were the best at capturing every vo C
the researchers threw at them so plants
definitely can remove some pollutants in
a laboratory test chamber but these
idealized lab conditions don't exactly
represent the air in your office stuff
like the amounts of light water and air
circulation are all going to be
different on top of that the lab plants
were purifying the air in a small area
some of the chambers in the NASA study
were less than a cubic meter and volume
that means for the same amount of
purification to happen in your house you
would need an indoor rainforest
one critic of the NASA study suggested
that to get the same effect in a typical
home you'd need about 680 separate
plants there have been a handful of
other studies investigating the effects
of plants on indoor air quality but at
least one review published in 2014 has
attempted to take stock of the existing
reefs
and it concluded that while lab based
studies generally show some effect not
many have been performed in living
spaces and are the ones that have been
done haven't yield at a consensus so
don't count on your poor desk fern to
fix all of your indoor air problems
so a single spider plant on the
windowsill isn't going to fix that
stuffy air but even if plants aren't
doing that much for you many of them are
looking out for each other
in the wild plants are constantly
communicating and many of them have a
lot to say here is how plants talk to
each other with the help of some
friendly fungi
the internet connects more than half of
the world's population through an
invisible web of servers computers and
devices it's changed our lives in
countless ways by allowing otherwise
separated people to interact and by
providing access to vast amounts of
information but humans aren't the only
organism on the planet with an invisible
interconnected network while plants
might seem like isolated solitary
individuals they're capable of
communicating with each other sometimes
over considerable distances all thanks
to their special relationship with fungi
nearly all plant species we know of have
a mutually beneficial relationship with
soil fungi called mycorrhizae
mycorrhizae grow a network of small
branching tubes called a mycelium that
extends through the soil including
inside or around plant roots and these
allow the fungi to absorb nutrients from
the soil like nitrogen and phosphorus
which plants struggle to extract so they
basically barter in exchange for those
hard to get nutrients the plants trade
the fungi carbon in the form of sugars
and ultimately together both can thrive
when they otherwise wouldn't dis
symbiotic relationship between plants
and fungi was discovered in the early
1900's but it wasn't until nineteen
ninety-seven that we understood just how
deep this underground network goes
ecologist Suzanne Simard had a hunch
that plants weren't just sharing
nutrients with fungi but also with each
other to test her hypothesis she and her
colleagues infused trees in a forest
with a traceable radioactive form of
carbon and later took samples from
neighboring trees and it turned out that
many nearby trees had the radioactive
carbon - proving that plants could send
nutrients back and forth to one another
not only that they seemingly distributed
the nutrients where they were needed
most plants need light energy to turn
carbon dioxide and water into sugar and
oxygen
thanks to that magical process called
photosynthesis so those in shade have
less sugar to go around Simard found
that these shaded energy deficient trees
ended up with more of the radioactive
carbon than their sunbathing
counterparts so it's basically the plant
fungi equivalent of feeding the hungry
continued research into these
underground networks called common
mycelium networks has revealed that
plants are not only able to gain access
to more new trees
they can also engage in sophisticated
communication by talking chemically
through my Celia and it turns out
they're saying quite a bit generally any
seedling that's plugged into the common
mycelium network or CMN has a higher
likelihood of surviving and the plants
that are online are generally healthier
- researchers think this has to do with
having access to an early warning system
when a plant's attacked it releases
chemicals that tell nearby plants
something bad is coming their way this
communication happens with airborne
compounds but also through a CMS and
other plants heed this warning for
example when tomato plants are connected
by a CMN and one plant is attacked by a
pest nearby plants will activate their
defenses before the pest reaches them
scientists are only just starting to
understand how important these plant
networks are they've discovered that
entire forests can be interconnected but
like with our internet connectivity
throughout an ecosystem isn't evenly
distributed older larger trees are more
connected kind of like some servers in
the human internet these highly
connected trees are called hub or mother
trees they have big root networks that
host a greater diversity of mica Raizel
fungi and that allows them to interact
with a lot of other plants they do play
favorites though scientists have shown
that they can send care packages of
extra nutrients to their kin to help
them survive which is how they got the
mommy moniker and they can also help
forests transition during times of
change when they're injured or dying
they release a surge of carbon into the
network which nurtures the next
generation of trees even if there are
different species of course no internet
is complete without hackers some plants
can claim territory and influence
community dynamics by sending toxins
into the CMN black walnuts will use
these networks to release toxins into
the soil for example those that are
immune to the toxins thrive while others
struggle or die off and harmful worms
parasitic plants and fungi can find
their way to the plants they target by
following chemical trails emitted by the
mycorrhizae underground it's amazing to
think that this chemical information
superhighway was right below our noses
for eons and yet we had no clue but now
that we can finally plug in it might
just help us connect to the planet's
flora in my
more constructive ways knowledge of this
interconnectivity is helping improve our
relationship to plans including things
like forest conservation and agriculture
for example preserving the highly
connected mother trees from
deforestation ensures Michael Raizel
fungal diversity and helps forest
regrowth happen more quickly and farming
in soil with a cm n means plants can
warn each other of invading pests which
might reduce the need for pesticides
like what the human Internet the
Internet of the earth increases security
awareness and knowledge for those
connected to it including us
so plants are just talking to each other
all the time and honestly that kind of
worries me because some plants are
keeping really big secrets here's Hank
with a terrifying secret about bananas
first the good bananas are healthy
packed with nutrition and energy they
fit in your hand and give nice little
cues when they're perfectly ripe and are
easy to peel and eat shocking statistic
the banana is Walmart's number one
selling item not the potato chip not
coca-cola not 50 shades of grey bananas
they appear to be so perfect for human
consumption that Kirk Cameron attempted
to use them to prove the existence of
God of course this banana was not
created by God or really even nature
bananas at least the ones that you see
at the store were created by people
don't get me wrong there are wild banana
plants lots of them they're native to
South and Southeast Asia and there are
dozens of species and thousands of
varieties they're just not the ones we
eat some of those species as you might
suspect have seeds
that's what fruits are their fleshy
bodies containing seeds so you might
wonder why have you never eaten a banana
seed well you have kinda in cultivated
bananas the seeds have pretty much
stopped existing if you look closely you
can see tiny black specks those are all
that's left and they're not fertile
seeds if you plant them nothing grows
today's bananas are sterile mutants I'm
not trying to be mean that's just the
truth unless you were alive in the 1960s
hats off to all those older scishow
viewers out there every banana you have
ever eaten was pretty much genetically
identical this is a Cavendish the
virtually seedless variety that we all
eat today but it wasn't always our
banana of choice until the 1960s
everyone was eating the same banana it
was just a different banana the grow
Michelle a bigger sweeter fruit with
thicker skin he might notice that banana
flavored things don't really taste like
bananas well they do they taste like the
girl Michelle the genetic monotony of
the Grove Michelle crop was its undoing
a fungicide resistant pathogen called
the Panama disease began infecting girl
Michelle crop but the time growers
understood how vulnerable their crops
were the grown Michelle variety was all
but extinct the entire banana industry
had to be retooled for the Cavendish
since they're seedless the only way to
reproduce them is to transplant part of
the plant stem and for the last 50 years
we've been good with the Cavendish
because it's more resistant to the
Panama disease however somewhat
terrifyingly a strain of Panama disease
that affects the Cavendish
we all eat has been identified a global
monoculture of genetically identical
individuals is a beautiful sight to a
pathogen the fungus only has to figure
out how to infect and destroy a single
individual and suddenly there's no
diversity to stop it or even slow it
down that's led to a lot of scientists
worrying about or even predicting the
outright demise of the Cavendish this
wonderful most popular of fruits might
completely cease existence the good news
is we now have a much better
understanding of genetics epidemics
fungi and pathology scientists and
growers have already taken steps to
protect the Cavendish some growers are
creating genetically different bananas
that might replace the Cavendish crop if
it fails while scientists are attempting
to genetically engineer Cavendish plants
with immunity to Panama disease plus we
learned a lot from the grow Michelle
debacle infected fields are quickly
being destroyed and new crops are grown
from pathogen free lab-grown plant stock
so thanks to the people who work
tirelessly to grow and harvest bananas
and bring them to us so that we can
offer them inexpensively to our
employees and thanks to the growers and
scientists working tirelessly to make
sure that they don't go the way of the
gros Michel
so bananas as we know them are mutants
and they're basically one fungus away
from extinction that is terrifying
and speaking of terrifying plants how
about plants that eat meat because
that's a thing here's Michael with the
scoop
Darwin's fascination with drosera a kind
of plant known as a Sun do stemmed from
its ability to capture and digest
insects she categorized it and other
plants like it as insectivorous plants
we know them today is carnivorous plants
because well they're not that picky
several species of the plants have been
known to trap and digest frogs and even
small mammals you've probably heard of
the Venus flytrap but did you know that
it's just one of more than 600 known
carnivorous plant species with more
discovered every year scientists
generally look for two things when
defining a carnivorous plant it has to
be able to absorb nutrients from a dead
animal and it must have some adaptation
that uses to attract capture kill and
digest its prey but where do these
adaptations come from and why would a
plant need meat when it gets its energy
from the Sun for free
well while most plants get their
nitrogen and nutrients from soil through
their roots carnivorous plants are
typically found in swampy environments
like bogs where water is constantly
washing those nutrients away so they get
their nitrogen from animal tissue
absorbed through glands and they're
specially modified leaves how exactly
they do this varies widely among
hundreds of species and at least nine
plant families there are pitcher plants
for example which lure their prey with
sweet nectar into leaves that resemble a
long tube insects fall from the slippery
rim of the pitcher into what's known as
a pitfall trap this is filled with a mix
of rain water digestive enzymes and the
leftovers of previous prey not exactly a
fun way to die then there are
bladderworts which with over 200 species
make up the largest group of carnivorous
plants they use bladders shaped leaves
lined with trigger hairs and topped with
a sort of trap door when an insect
touches one of the hairs the door opens
and sucks in the victim within 15
minutes the prey is digested quite
efficient species of the sundews
described by Darwin act much like a
spider web luring and catching insects
with sticky drops disguised as nectar
but those drops contain a thick mucus
like substance that traps the prey on
the leaves sticky tentacles and the
venus flytrap is well known for a good
reason its eponymous trap activates when
an insect walks across the leaf and
applies pressure to its trigger hairs
but it doesn't initially close all the
way scientists believe that this is a
plant's way of letting smaller bugs
escape so it doesn't waste time
digesting a low nutrient meal instead it
closes a second time soon after using
enzymes similar to those in our stomachs
to slowly digest its prey
unlike other carnivorous plants the
venus flytrap can take up to ten days to
finish its meal for more than 100
50 years carnivorous plants in their
astounding diversity have fascinated and
perplexed botanists and until the late
1980s many scientists thought they all
shared a common ancestor but studies in
the last 25 years have shown that
carnivore as it's called evolved
independently at least six times within
five orders of plants carnivorous plants
are a pretty wonderful example of
convergent evolution in which unrelated
organisms developed similar traits in
response to their environment in this
case nutrient poor swamps and bogs all
around the world
fine so some plants eat meat and by some
I mean hundreds but who's counting
actually maybe plants as Hank explains
now you might have heard the plants can
count and yes I know this sounds like a
silly question to ask if it is true but
even the New York Times has called Venus
flytraps a plant that can count the
thing is they can but it's not counting
the way you know it which is to say they
don't have some kind of mental
representation of numbers in their
brains because as far as we know they
don't have brains they're not sentient
we're not talking like Groot here in
Groot count there's evidence for some
sort of counting mechanism in plants
though and a lot more work needs to be
done to properly understand it the whole
idea of counting plants went viral after
a 2016 paper and Current Biology the
title of the study itself literally has
the words venus flytraps count in it so
like you can't really blame the headline
writers here and yes we're talking about
those infamous fly traps that snap up
unsuspecting flies with their leafy
mouths you see the study found that an
insect needs to bump small trigger hairs
on the plant's leaves at least five
times before the plant would begin
secreting enzymes to digest it and this
built on knowledge already known within
the botany community that the plants
close those leaf bouts of an insect
bumps trigger hairs twice within 15 to
20 seconds if the plants can discern one
or five different triggering x' well
they're counting right and presumably
that means they think about and process
numbers somehow which would mean that
they have to think well as awesome as
the idea of sentient plants might seem
they're probably not thinking or really
understanding numbers not in the way
that we do anyway you see your brain
actually has specific neurons that fire
when you look at certain quantities one
set will fire when there are three lemon
drops on a plate another when there are
four intriguingly these are different
than the neurons that fire when you
simply look at numbers written out but
both seem to give you some kind of
mental representation of the amount it
is doesn't seem to be much concrete
evidence for these kinds of mental
representations of numbers in plants
though at least one study says you can
never be sure the plants do have our
sophisticated biological mechanisms that
enable them
react to changes in their environment
and while these responses may look like
plant intelligence at first glance they
fall short of what you and I might
associate with conscious thinking there
are some similarities though like both
you and plants can transmit information
quickly thanks to electrical signals
called action potentials the process
isn't exactly the same for plants and
humans since the chemicals involved are
a little different so they're similar
and they are how a flytrap counts it
generates and transmits action
potentials every time a trigger hair is
touched a number of action potentials
not only dictates if a trap should close
but also how much digestive juice it
should secrete presumably more
triggering implies a larger insect that
will require more enzymatic activity to
break down basically having a measure of
the size of their meal lets them meter
their investment in it so they don't
waste energy but the electrical
communication networks in plants are
much simpler than in humans and other
animals they're not considered true
nervous systems so signals never arrive
at some central hub or brain where
they're processed and translated into
action so even if we know that venus
flytraps can count and why how it counts
is still up for investigation and it's
not just the Venus flytrap many other
plants use action potentials and other
types of electrical signals and even
without brains plants can do things that
involve some pretty impressive math a
2013 study used mathematical models to
show that a small mustard relative can
do something akin to division to
partition its food so it lasts through
the night other plants have the
equivalent of an internal thermostat
that lets them regulate their
temperature so yeah so plants can't
really count numbers or think about them
the way that we do but they're still
pretty remarkable and they still know
how many times they're little hairs get
shoved around by a fly
okay if nothing else they're not
counting how many days you forgot to
water them thanks for watching this
leafy compilation and thanks to all of
our supporters on patreon who helped us
make all these episodes and if you want
to help us keep making contents like
this
head over to patreon.com/scishow to
learn more
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