THE ATMOSPHERE AS RELATED TO VEGETATION. 103 
other in penetrating it. In case a membrane is moistened 
with water or other liquid, or by a solution of solid mat- 
ters, this would still further modify the result. 
Absorption of Gases by the Plant.—A few words will 
now suffice to apply these facts to the absorption of the 
nutritive gases by vegetation, The foliage of plants is 
freely permeable to gases, as has been set forth in “ How 
Crops Grow,” p. 289. The cells, or some portions of their 
contents, absorb or condense carbonic acid and ammonia 
in a similar way, or at least with the same effect, as potash 
absorbs carbonic acid. As rapidly as these bodies are 
removed from the atmosphere surrounding or occupying 
the cells, they are re-supplied by diffusion from without ; 
so that although the quantities of gaseous plant-food con- 
tained in the air are, relatively considered, very small, 
they are by this grand natural law made to flow in con- 
tinuous streams toward every growing vegetable cell, 
