THE PLANT WORLD 159 
animals, as we know them, had not yet become 
differentiated. 
Among plants, as distinguished generally from 
animals by the production and abundant use of chloro- 
phyll and of cellulose, we have still existing on the 
Earth a range of forms extending from almost the 
most primitive organism that we can imagine up to 
the splendid Seed Plant, specialized in a hundred ways. 
Every pool, every soil, swarms with bacteria, the 
lowliest form of life—organisms exceedingly minute, 
exceedingly simple, and capable of existing under 
highly diverse conditions both physical and chemical. 
Thence we can trace an irregular ascending scale 
through the Fungi, the Algz, Mosses, Horsetails, 
Ferns, and Club-mosses, to the Conifers, and on to 
the highest of the Seed Plants, which exceed in their 
beauty of structure and complicated life anything 
that has gone before them. In fact, as Theophrastus 
says, your plant is a thing various and manifold. And 
this existing vegetation with its thousand forms is 
but the present manifestation of the vital activity 
which has populated the earth during tens of millions 
of years. The oldest rocks which have been pre- 
served to us in such a condition as to yield remains 
of plants and animals in a recognizable form are 
those known as Cambrian, the deposition of which 
occurred at a period which geologists have variously 
calculated as from, say, 20 to 100 or more millions of 
years ago. Yet even at that immensely remote 
period, life, both vegetable and animal, was already 
abundant and diverse, as well as highly organized. 
As Darwin long ago pointed out, the geological 
record does not go back nearly far enough to allow 
