TWO 
THE CLASSIFICATION OF FOSSIL PLANTS 
I F WE knew everything about the evolution of plants, 
we could easily map all the ramifications of the 
great branches springing from the evolutionary tree in 
the plant kingdom. We could trace the plants of the 
present day back to their common origin and establish 
their relationships with each other. We could definitely 
classify these relationships and arrange all the plants 
under the heading of stems, orders, families, genera, and 
species, as we have been able to do much more completely 
with the different forms in the animal kingdom. 
The actual state of affairs, however, is far from this 
ideal condition. It is true that we have classified nearly 
all the living plants, but we know only a comparatively 
few of the myriads that must have existed in the course 
of the hundreds of millions of years that plant life has 
been on earth. The world’s present flora contains some 
300,000 species. If we imagine them as the base of an 
inverted pyramid, and their origin as the point on which 
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