EVOLUTION 161 
5. All plant relationships are genetic, and these rela- 
tionships are up and down the genetic lines. 
ORIGIN OF PHYLA 
211. If now we inquire as to the origin of phyla we may 
formulate our answer in several ways. Stated philo- 
sophically we may say that a phylum originates with 
the incoming of a new idea. Stated structurally, it has 
its beginning with the development of a dominant mor- 
phological peculiarity. Stated taxonomically, its initial 
point is indicated by the appearance of a new character. 
So every phylum is the result of a development which 
differs from that which preceded it because of the incom- 
ing of a new idea: this dominant idea was manifested 
structurally by a divergence from the previous lines of 
evolution and this point of divergence became the actual 
origin of the new phylum. As long as this idea and its 
structural expression dominate, so long does the phylum 
extend, and when a still newer idea comes in and attains 
dominance, a still newer phylum has its beginning. So 
we say that a phylum originates with a divergence which 
is the expression of a new idea, or in other words a “‘ tend- 
ency”’; and this in taxonomy we call a “new character.”’ 
Tue PLACE OF PLANTS IN TIME 
212. As stated above, plants have been in existence a 
very long time, and as some references will be made in the 
following chapters to particular periods of time it is 
necessary here to give a table showing the divisions of 
earth time (‘‘geologic time”) as recognized in recent 
treatises, with suggestions as to their vegetation. In this 
table no attempt is made to indicate the relative lengths 
of different periods. 
11 
