ADAPTATIOxX TO WATER 



149 



stomata is well illustrated l)y Ranunculus sceleratus, a species of 

 wet places, in which the stomata are more abundant upon the 

 upper surface. Plants grown in water with the leaves floating, 

 and in soils containing 40%, 30%, 15%, and 10% of water, showed 

 respectively the following results wdth respect to the stomata of 

 the two surfaces: upper 20, lower 0; upper 18, lower 11; upper 11, 

 lower 8; upper 10, lower 6. 



Reduction in the number of stomata gives sufficient protection 

 only under moderate conditions of dryness. Where dryness is 

 intense, the guard-cells are usually found sunken below the epi- 

 dermis, either singly or in groups. Sunken stomata are generally 



Fig. 46. Upper epiderm of a submerged (1 ) and an aerial leaf (2) of a plant 

 of CalKtriche bifida, showing the decrease in the number of stomata. 



found at the bottom of chimney-like ojienings. which are some- 

 times almost completely closed above. When the stomata are 

 sunken in groups, the cavities are commonly filled with protective 

 hairs, or closed by them. In ])oth cases the protection is very 

 effective. The guard-cells are screened from the intense action 

 of light and heat, and from the dry air. The rays of the sun can 

 enter the chimney-shaped chambers only for a few minutes each 

 day, and are practically excluded from the stomatal hollows, which 

 are filled with hairs. The influence of dry winds is likewise almost 

 wholly eliminated. This is true in a less degree for stomata which 

 are arranged in furrows protected by intervening ridges. The 

 cuticle often forms valve-like projections upon the guartl-cella 



