1889.] PUBLIC DOCUMENT — No. 4. 39 



These constituents can be roughly separated into two 

 classes : 1st, Those removed from the soil ; 2d, Those re- 

 moved from the soil and atmosphere. The water and ash, 

 or 79.85 per cent of the total, comes from the soil, as also 

 some little of the remaining constituents. The carbon comes 

 from the atmosphere directly, and is built up into the 

 various carbohydrates. It is not necessary to our purpose to 

 calculate the exact relations, but only to call attention to the 

 fact that in the plant, water, which is taken from the soil, 

 constitutes fully 79 per cent of the weight of the living 

 plant, while the ash and nitrogen combined do not exceed 

 1.14 per cent, and the phosphoric acid but .08 per cent, and 

 the potash but .28 per cent. 



Transpiration in plants is the escape of aqueous vapor 

 that has accumulated in the intercellular spaces, through the 

 stomata of the leaves, and it varies in amount with the char- 

 acter of the plant, the moisture of the atmosphere, the in- 

 tensity of the light, or the temperature, wind, etc. ; or, in 

 other words, upon those changeable conditions that occur 

 between plants and their relations towards environment, 

 which are principally, in turn, the relations which find ex- 

 pression in the concrete term climate. It is hence difficult 

 to determine the average amount of this transpiration ; but 

 we can readily determine the amount of water thus given off 

 by individual plants under given conditions, and can readily 

 reach the conclusion of its enormous proportions and im- 

 portance. Prof. Boussingault * found that in the case of the 

 Jerusalem artichoke in a pot, each square metre of foliage 

 exhaled hourly 65 grammes in the sunshine, 8 grammes in 

 the shade, and 3 grammes at night. Wiesnerf found that 

 from 100 square centimetres of green maize leaf there were 

 transpired in one hour: in darkness, 97 milligrammes; in 

 difiused daylight, 114 milligrammes; and in sunlight, 785 

 milligrammes. In some experiments carried forward at 

 Rothamstead,! Sir J. B. Lawes reports that, from March 

 19 to September 7, the quantity of water given off by 



* Popular Science Monthly, Jan., 1879, p. 365. 



t Ann. de So. Nat. (6), 14, 1887. Goodale Phys. Bot., 278. 



X Hort. Trans., 1850, p. 45. 



