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3. Early Land Plants 
In passing from the transparency devoted to Algae to that show- 
ing Early Land Plants, we are witnessing a most momentous 
ab) 
evolutionary step, one that occurred in the early Paleozoic and 
which, eons later, made possible the evolution of warm blooded 
animals, and still later enabled the human species to become what 
we call civilized. 
In the evolution of both plants and animals the transfer of the 
principal theater of their activities from the sea to the land was 
certainly from the point of view of humanity their greatest evolu- 
tionary change. 
The exact steps in this change of habitat, either among animals 
or plants, we do not know, nor whether the terrestrial plants had a 
single (monophyletic) or diverse (polyphyletic) ancestry among 
the marine algae. It is clear, however, that algae were the an- 
cestors of terrestrial plants, but beyond this cardinal fact all else 
is speculation. Certainly the most ancient known land_ plants, 
which might be considered to constitute a Pteridophytic (Fern 
tvpe) or better perhaps an archegoniate + evolutionary stage, 
present unmistakable evidences of an aquatic ancestry. They 
have so many common features that community of origin seems 
almost certain. 
We may pause for a moment to consider the problems which 
the emerging plants had to face in order to adapt themselves to a 
terrestrial existence. In their ocean home they lived in a medium 
that furnished mechanical support, one rich in food but somewhat 
deficient in light, roots except for anchorage were not required, 
no desiccation-resisting stage was necessary for dispersal. On 
the land the air gave no mechanical support nor salts for food. 
Although there was plenty of light, the plants were always faced 
with a deficiency of water, and they must also evolve some means 
for securing dispersal. 
In addition to serving for anchorage, roots became absorbing 
organs to secure the necessary water and food salts; the surface, 
except for minute openings (sfomata), became encased in cutin, 
impervious to gases, in order to conserve the water supply. In 
1 Mosses and Ferns and their relatives are, together, called Archegomiates 
Is are produced in an organ called an archegonium. 
hs 
because their egg-ce 
