EXPERIMENTAL EVOLUTION 123 



show their descent and their relationship to each other. 

 Without evolution there might be any number of arbitrary 

 systems; on the basis of evolution there can, in the end, 

 be but one true system, which all students must accept, 

 because it will be a true record of what has actually oc- 

 curred in the history of development of the plant or animal 

 world. In other words, if our knowledge should ever be- 

 come sufficiently complete and exact, the classification of 

 plants would give a summary a bird's eye view of the 

 course of evolution and the history of development. To 

 approximate this end is one of the largest problems of botany. 



