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. 
