52 PLANT RELATIONS. 



that the water glances off at once from the surfaces of 

 some leaves, runs off more slowly from others, and may be 

 more or less retained by others. 



In this same connection it should be noticed that in 

 most horizontal leaves the two surfaces differ more or less 

 in appearance, the upper usually being smoother than the 

 lower, and the stomata occurring in larger numbers, some- 

 times exclusively, upon the under surface. While these 

 differences doubtless have a more important meaning than 

 protection against wetting, they are also suggestive in this 

 connection. 



