470 



ECOLOGICAL GROUPS 



and there are many ferns and mosses which nourish in such 

 situations. Shade plants commonly have large pale leaves, and 

 generally (except in ferns) the leaves are not much cut or lobed 

 (Fig. 364, A). Sun-loving plants, on the other hand, usually 



have comparatively 

 little leaf surface, and 

 the leaves are often cut 

 into narrow divisions 

 (Fig. 364, B). Appar- 

 ently the broad leaf 

 surfaces in the one 

 class are to expose 

 many green cells to the 

 light for starch making, 

 while in the other class 

 the slender leaf divi- 

 sions expose enough as- 

 similating cells, and at 

 the same time the nar- 

 rowness of the division 

 permits plenty of light 

 to penetrate to the 

 plant's lower leaves. It 

 is also, doubtless, much 

 easier for leaves like 

 those of the yarrow, 

 the dog fennel, the 

 tansy, the carrot, and 

 their like to withstand the action of severe winds, to which they 

 are often exposed, than it would be for leaves like those of 

 the jack-in-the-pulpit, the trilliums, the lily of the valley, and 

 similar leaves. 



447. Sun leaves and shade leaves on the same plant. On 

 plants of the same species, or even on the same individual, sun 

 leaves and shade leaves often differ widely-. On comparing the 



FIG. 364 



A, a shade plant (Clintonia) ; B, a sun plant, 

 dog fennel (Maruta) 



