14 AGRICULTURE. 



filled up, so that as water is constantly going in by way of the 

 roots, it must be passing out by some way. 



When the soil becomes very dry and the plants, as we say, 

 suffer from drouth, the first place where we observe the effect 

 is in the leaves. These droop and wilt and lose their freshness, 

 and soon after watering they become fresh-looking again. 



Let us take a clear bottle and wipe it out so as to have it 

 perfectly clear, clean and dry on the inside. Then we carefully 

 place it over the branch of a growing plant so as to have the 

 bottle pretty well filled with leaves. We leave it there, fastened 

 up securely, for a time ; after a while we observe a fine film on 

 the inside of the bottle. When we take it off we notice that 

 the bottle is damp on the inside, some water has been depos- 

 ited upon it from the leaves. We observe the same kind of a 

 film on a piece of looking-glass when we breathe upon it. In 

 fact, we can take a piece of dry looking-glass and fasten it 

 to a plant leaf and get a faint film of moisture from the leaf as 

 from our breath. Further, if we try first the upper side of the 

 leaf and then the under, we shall find that the moisture comes 

 almost entirely from the under side. 



We conclude, then, that the water passes out by the leaves 

 and principally from the under surface. If we had a microscope, 

 that is ail instrument for making small things appear large, we 

 could examine the two sides of the leaf of any plant, and then 

 we would observe that on the under side there are a great 

 many little mouths, or pores, or openings whereby the water 

 can pass out, and that these are drawn up smaller as the air 

 becomes drier so as to prevent too great loss of water. Each 

 of these mouths or pores is called a " stoma," and when we 

 speak of two or more we call them " stomata." 



We have called these mouths or pores ; they are openings 

 through which the plant breathes, and they are generally on the 

 under side of the leaf, several hundred or several thousand on 

 every leaf. In the case.of such a plant as the water lily, whose 



