AGRICULTURE ON CLIMATE. 179 



As a rule, the exhalation from vegetation will be in pro- 

 portion to the amount of foliage and the luxuriance of its 

 growth ; least from the mossy, close-cropped pastures ; more 

 from the thrifty growing grains and grasses ; still greater 

 from the rampant growing corn, and most from the forest, 

 with the moisture-lovino- air floating through its one hundred 

 or more feet of perpendicular growth. The amount of ex- 

 halation from plants varies with the temperature and moist- 

 ure of the surrounding air. 



Experiments have shown that a sunflower with thirty-nine 

 square feet of leaf surface gave off in twenty-four hours 

 three pounds of water ; grass sod, per square foot, one and 

 one-half pounds per twenty-four hours. 



In recent experiments a dwarf-bean exhaled during twenty- 

 three days in September and October thirteen times its 

 weight of water, which is more than half its weight each 

 day ; and if more than half its weight each day on an average 

 in September and October, it would no doubt exhale double 

 its weight in one hot day of July or August. An experiment 

 has proved it. Sir J. B. Laws has proved that most plants 

 durino; the few months of their growth exhale more than two 

 hundred times their weight of water. That would equal five 

 thousand tons of water from an acre of ensilage corn, sup- 

 posing the crop to be twenty-five tons ; and even that, I 

 doubt not, is an under-estimate. 



EVAPORATION. 



Professor Burrill of Illinois says, " The amount of water 

 exhaled from the leaves of trees in dry, hot weather is prodig- 

 ious, — vastly greater than any one not acquainted with the 

 results of experiments upon the subject supposes. As near 

 as can be made out from investigations upon small plants 

 in pots, a large-sized forest tree throws into the atmosphere 

 every favorable summer day about fifty barrels of water, 

 counting forty gallons to the barrel. One apple tree twenty 

 years old may be estimated to be one-fifth as large, and to 

 exhale ten barrels of water each clear and breezy day of 

 June, July and August. This seems incredible, but it is not 

 above the accurately determined facts with potted plants of 

 many kinds." 



