And also to keep them together.
But on land, they have to defy gravity now.
So they need to be pulling up the water and
the nutrients to the most distilled part of the tissues.
So this formation of a vascular system was really, really crucial for
these early plants.
>> So we have create some kind of a negative pressure gradient within these
capillaries then to pull the water from the soil from low down up to
in the case of cooksonia just a centimeter or two away from the ground.
>> Absolutely and a big part of that is through transpiration.
And that's really what drives that negative pressure.
>> Okay.
And so the transition then from these small,
little podlike plants to what we think of now,
trees, grasses.
How did that happen?
>> Well it was a definitely a very gradual process.
So you start to see, so as I said.
The Cooksonia occurred during, around the Mid Silurian.
And it's not really until the Devonian that you start to see leaves forming.
And then later on in the Late Devonian you start to see
the secondary xylem starting to form, which is wood.
And once wood was produced and
you have these leaves that can increase the surface area for photosynthesis.
Then you can start to get the really giant trees that you start to see
in the Carboniferous.
>> We just talked about the five different adaptions that plants had to make
in order to come onto land.
Is this similar, different to what the transition that animals had to make
to come on land as well?
Well, essentially, some of the main features that plants had to adapt,
animals had to adapt, also.
So, for example, they had to create some sort
of outer covering to prevent them from desiccation, just like plants did.
So, plants developed a cuticle, arthropods, a hard exoskeletons,
and then, with amphibians to reptiles, a very thicker epithelial tissue.
And that prevents the cicaction.
But also you have things like respiration structures that had to be developed.
Because it's much easier to get water from the.
Get oxygen from the water.
As opposed to through the air.
And so a specialized structure had to be developed.
Once you make that transition to the air.
But also reproduction.