540 STRUCTURE AND LIFE HISTORIES 



that they have a chance similarity in the number of 

 stamens. In like manner we may group together plants 

 with red flowers, blue flowers, or pink flowers, as is often 

 done in " popular" guides to the wild flowers. This has 

 its value, but it tells us really nothing about the significant 

 relationship between plants, does not help clear up our 

 own ideas, does not show the gaps in our knowledge and 

 tell us where to search for new facts to fill up the gaps. 

 Evolution, by showing that plants are all related to each 

 other by descent, just as are the members of a large family 

 of persons, discloses to us the only true basis of classifica- 

 tion the plan that endeavors to arrange all plants so as to 

 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 

 worlds. 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. 



