DIV. I 



MORPHOLOGY 



181 



The more uniformly favourable for vegetation the climate is 

 throughout the year (as in the moist tropical regions) the more do 

 evergreen woody plants preponderate, though evergreen perennial 

 herbs often with subterranean shoots are also present. On the other 

 hand, as the periodicity in the climate becomes more extreme, as in 

 the steppes with a long dry period or in climates with severe winters, 

 the percentage of tropophytes with marked protective arrangements 

 increases, while annual plants and geophytes preponderate among the 

 herbs. 



(b) Adaptations for obtaining Light ( 84 ) 



In the luxuriant vegetation produced under favourable climatic 

 conditions plants of large or gigantic size are met with. As mentioned 



FIG. 208. Portion of stem and leaf of the common Pea, 

 Pisum satimm. s, Stem ; ;i, stipules ; b, leaflets of the 

 compound leaf ; r, leaflets modified as tendrils ; a, floral 

 shoot. (nat. size. After SCHENCK.) 



FIG. 209. Lathyrus Aphaca. 

 s, Stem ; , stipules ; 

 b, leaf tendril. ( nat. 

 size. After SCHENCK.) 



above, the primeval tropical forest is composed of such large trees, 

 beneath the shade of which larger and smaller evergreen shrubs and 

 evergreen herbaceous plants live. The direct sunlight is in large 

 part intercepted by the foliage of the upper strata of this vegetation. 



The cuticle of the leaves of tropical trees is often smooth and reflects a portion 

 of the light, giving rise to the characteristic glitter on the foliage in these regions. 

 This is possibly a protective arrangement against too great insolation. Other 

 adaptations to the same end were considered on p. 169. 



The smaller SHADE PLANTS of the primeval forests and also of our 

 native woods have usually large leaves, and are adapted to the assimila- 

 tion of carbon dioxide in light of low intensity. 



In the struggle for light two groups of cormophytes of character- 

 istic construction have emerged, in addition to trees and shrubs. 



