Classification of Plants 



201 



are separated by differences in parts which alter little or slowly. 

 A plant's immediate needs are met by its vegetative organs (root, 

 stem, leaves). These change remarkably under varying condi- 

 tions of climate and soil. The reproductive parts, concerned 

 with the future needs of the race, are less affected by these out- 

 ward conditions. Consequently the flower is of more import- 

 ance in distinguishing main groups. Besides cohesion of the 

 floral parts, and the position of the ovary, the seeds, their number 

 and position, the number of coats, and theipresence or absence of 

 endosperm, are important factors. The composition and shape 

 of the leaves are less valuable ; but their position, venation, and 

 presence or absence of stipules are of importance in dis- 

 tinguishing lower groups. 



Fig. 194. — Diagrams to illustrate the morphology of flowers. A, hypo- 

 gynous ; B, perigynous ; C, epigynous. 



It is upon the degree of cohesion and adhesion that 

 Bentham and Hooker make their main divisions in the classi- 

 fication of Angiosperms. In Thalamifljrce and DisciflorcB the 

 sepals are usually distinct and separate ; the ovary is always 

 superior, that is the other floral parts are situated below the 

 ovary (hypogynous). In Disciflorae the receptacle is expanded 

 into a disk. In Calyciflone the receptacle is more or less ex- 

 panded and hollowed, gradually becoming tubular and surround- 

 ing the ovary. If this tube is free from the ovary, the floral 

 cycles are perigynous ; if it is joined with the ovary the 

 perianth and stamens are epigynous. 



In classifying a plant, a synopsis is useful for identifying 



