436 ZESSOJSrS WITS PLANTS 



562. The evolution systems must be the systems 

 of the future, for they afford the convenience of a 

 classification at the same time that they suggest 

 genealogical relationships. The teacher must be 

 warned, however, that it is impossible to represent 

 a perfectly true classification, — that is, a natural 

 one, — in a book, from the fact that the classifica- 

 tion must be lineal or successive, whereas we know 

 evolution to have been a series of divergencies. 



563. In other words, evolution has not pro- 

 gressed in a line, but in the form of a tree. 

 Branch after branch has been given off. Some 

 branches have long since reached their develop- 

 ment and are dying out ; others are still growing. 

 We must not expect, therefore, that present types 

 of flowering plants came from present types of 

 flowerless plants, merely because the latter are 

 placed first or lowest in the scale of classification. 

 Probably both came from a common ancestor in 

 remote time ; and this ancestor may be lost. 



564. The present forms of vegetation, then, 

 are the tips of the branches of the tree of life. 

 Therefore, the "missing links" are to be sought be- 

 hind, not between : they are ancestors, not inter- 

 mediates. 



Suggestions. — Wlien the pupil has acquired a good knowledge 

 of the parts of the plant, he will be interested in the bolder strokes 

 in schemes of classification. Let the teacher take any systematic 



