SHADE PLANTS 247 



such plants live, the difPase nature of the illumination 

 has probably the most powerful influence, not only on 

 the external form, but on the internal structure of the 

 plant (see p. 202). The dependence of the green 

 plant on light, for the maintenance of assimilation 

 through the agency of the chlorophyll, or green 

 pigment of the leaves, etc., has been already 

 explained (p. 10). 



This being so, we should naturally look to the 

 leaves of shade plants for some indication of the 

 conditions under which they grow. In many cases, 

 but not by any means all, it will be found that the 

 leaves of shade plants are larger, broader, and thinner, 

 and at the same time more intensely green than those 

 of plants thriving fully exposed to the sun. They are 

 often hairless or only slightly hairy, but no rule can 

 be laid down as to the presence, or absence, of hairs 

 on the leaves of shade plants. Some, while hairless 

 on the upper surface, are covered with a thick hairy 

 felt on the lower. The leaves of the Lily of the 

 Valley, the May Lily (Plate XL VII., Fig. 2), and 

 the Two-flowered Violet (Plate XL VI., Fig. 2) are 

 quite typical of a shady habitat. We also find in 

 a number of cases, that where the shoots bear many 

 scattered leaves, the successive leaves are separated 

 by fairly long internodes, as in Solomon's Seal. 



If we examine closely any large Spruce forest, the 

 influence of sunlight can be readily seen. Where the 

 trees are dense and their branches interlace over- 

 head, the carpet of " needle " leaves will be found to 



