52 PLANT STUDIES 
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. 
