THE ANGIOSPERMAE : LEAVES 



lOI I 



B 



Fig. 999. — Lit/iops sp. Epidermal cells showing 

 focal spots of light on the inner walls. 

 A, In the natural state. B, After decalcifica- 

 tion. 



the inner tissues and the environment, and they seem to be fundamental to 

 land life, since we find them, or structures analogous to them, in all land 

 plants, from the Bryophyta upwards. From this standpoint their functioning 

 is dealt with in Volume III, in relation both to photosynthesis on the one hand 

 and to transpiration on the other. Here we shall consider them anatomically. 

 Stomata in land plants are chiefly distributed on the lower leaf surface, a 

 fact which has been interpreted as giving protection against the blocking of 

 the stomatal opening by dust, rain, and dew. There are, however, many 

 exceptions in which stomata occur on both surfaces, especially among those 

 plants, principally Monocotyledons, which have leaves held vertically. Centric 



