56 



ELEMENTS OF AGRICULTURE 



find that the upper side, which is the one turned towards 

 the sun, is different from the lower side. By examining 

 the lower side with a good magnifying glass you will 

 notice many small openings in the leaf. These little 

 mouth-like openings are called stomata, and have the 

 power of opening or contracting. Fig. 10 shows some 



of these stomata. Through 

 these openings the plant 

 gives off water and takes in 

 food from the air. Water 

 thus given off by the plant 

 is said to be exhaled. The 

 plant takes in or absorbs 

 water through its roots and 

 exhales it through its 

 leaves. This giving off of 

 water through the leaves is 

 also called transpiration, 

 and may be compared to 

 the giving off of water 



Fig. 10.— Stomata, or breathing +l r ,. rmo 4 1 +V, P -]?;„ n f Vmmin 

 pores : A, under side ofleaf highly tlllOUgll Tile SKin 01 Human 

 magnified; stomata shown at «; i • „ i • i » ^ ii j _^„ 



small hairs in leaf at h. bemgs, which is called per- 



B, section through stomata, .. .,,. , » 



highly magnified; 8, mouth of SpiratlOn. \Lhe amount 01 



stomata; a, air space in the leaf; , . 



0, cells which as they expand or water which plants give 



contract, open or close the sto- t ° 



mata. off through their leaves, 



of course, varies, but most growing crops give off 

 large quantities of water. On a dry, hot day grass 

 plants have been known to exhale their own weight of 

 water in twenty-four hours. Experiments conducted in 

 Germany have shown that plants, for every pound of 

 dry matter, require, during the time they are growing, 



