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 ovar\-, the seeds, their number 

 and position, the number of coats, and the^presence 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 Thatamifl irce and Discifloroe 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 Disciflorce the receptacle is expanded 

 into a disk. In Calycijione 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 



