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 begirming 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." 



The 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. 



