122 HEREDITY AND EVOLUTION IN PLANTS 



Scientific knowledge, in addition to being as accurate as 

 possible, is characterized by having an orderly arrangement 

 in one's mind, and this order is based on a logical, funda- 

 mental relationship between the facts and ideas. Only 

 by such an arrangement of our ideas are we able to under- 

 stand their relation to each other, their relative impor- 

 tance, and their real significance. Classification, there- 

 fore, is essential to all science. The very existence and use 

 of such words as oaks, maples, roses, indicate that men 

 have grouped or classified their ideas of certain plants 

 (e.g., red oaks, white oaks, black oaks, bur oaks, live 

 oaks, etc.), and have thereby recognized that certain kinds 

 resemble each other closely enough to be placed in one 

 group with a group-name. All the common names of 

 plants indicate the recognition of classes -a classification. 

 96. Evolution and Classification. Without the guiding 

 idea of evolution classification would be arbitrary and 

 artificial. Linnaeus classified plants on the basis of the 

 number of stamens they possessed, thus placing in one 

 group plants now known to be wholly unrelated, except 

 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 



