THE LEAF AS A PHYSICAL STUDY. 141 



water dail}' transpired is immense, and that forests make a damp 

 atmosphere for miles around, simply from this transpired matter. 



According to Hales, a cabbage presenting a surface of 2,736 

 square inches exhaled from da}' to day nineteen ounces, and on 

 some days as high as twent3-five ounces, and these days of twelve 

 hours only; a sunflower from twent}' to thirty ounces, etc., etc., 

 long lists being given. According to Johnston, tlie English 

 agricultural chemist, a field in crop to grain or grass will transpire 

 from 3,000,000 to 5,000,000 pounds of water in its season's growth ; 

 an immense amount, we must all acknowledge. We know that a 

 rainftill of one inch is equal to one hundred and one tons of water to 

 the acre. At this ratio, could all this evaporated water be returned 

 in the shape of rain, it would amount to an inch and a half or two 

 inches. If one acre of grass can give a result as wonderful as this, 

 what will be the effect of large tracts devoted to forestry ? In this 

 connection we cannot but admire the silent workings of Nature, as, 

 unseen and almost undetected, she carries on these stupendous 

 operations. 



The leaves of aquatic plants perform essentially the same offices 

 as those which have their habitat upon the land, and there is 

 reason for the belief that the\' in no small degree contribute to the 

 purification of the waters wherein they grow, and of which, in many 

 instances, both we and our cattle drink. When our various State 

 legislatures are called upon to pass laws regarding the purification 

 of streams, as in time the}' will be, and as is now being done in 

 Connecticut, we shall hear more and know more of the action of 

 the leaves of aquatic plants regarding this important office. 



We see carbon extracted from the air through the leaf, and 

 stored within the living tissues of plants, — a process universal 

 throughout the whole vegetable world. It is within our province 

 as inquiring agriculturists to follow it still further, and learn of its 

 action within the soil we cultivate ; for it becomes incorporated with 

 it, sooner or later, as organic matter, by the decay of vegetable 

 growth. During the decay a portion of the matter escapes in the 

 form of gas ; the remainder undergoes a slow process of combus- 

 tion, leaving tlie carbon as charcoal, in which form it always 

 remains one of the most indestructible elements. The agricultural 

 value of charcoal does not consist iu the fact that it is a component 

 of plants, but upon otlier offices of great importance which it per- 

 forms. It makes the soil retentive of manures, because it is one 

 of the greatest absorbents of gases known, receiving them not 



