^20 now cuors feki;. 



times greater amount. In olhor words, in llie cultivated 

 soils taken to the depth of 14 inches, there was found as 

 much carbonic acid gas as existed in the same hoiizontal 

 area of the atmosphere through a height of 7 to 110 feet. 

 The accumulation of such a percentage of carbonic acid 

 gas in the interstices of the soil demonstrates the rapid 

 formation of this substance, which must as rapidly diffuse 

 off into the air. The roots, and, what is of more signifi- 

 cance, the leaves of crops, are thus far more copiously fed 

 with this substance than were they simply bathed by the 

 free atmosjihere so long as the latter is unagitated. 



When the wind blows, the carbonic acid of the soil is 

 of less account in feeding vegetation compared with that 

 of the atmosphere. When the air moves at the rate of 

 two feet per second, the current is just plainly perceptible. 

 A mass of foliage 2 feet high and 200 feet * long, situated 

 in such a current, Avould be swept by a volume of atmos- 

 phere, amounting in one minute to 48,000 cubic feet, and 

 containing 12 cubic feet of carbonic acid. In one hour it 

 would amount to 2,280,000 cubic feet of air, equal to 7:20 

 cubic feet of carbonic acid, and in one day to 69,120,000 

 cubic feet of air, containing no less than 17,280 cubic feet 

 of carbonic acid. 



In a brisk wind, ten times the above quantities of air 

 and carbonic acid would pass by or through the foliage. 

 It is plain, then, that the atmosphere, wliich is rarely at 

 rest, can supply carbonic acid abundantly to foliage with- 

 out the concourse of the soil. At the same time it should 

 not be forgotten that the carbonic acid of the atmosphere 

 is largely derived from the soil. 



Carbonic Acid in the Water of the Soil.— Notwith- 

 standing the presence of so much carbonic acid in the air 

 of the soil, it appears that the capillary soil-water, or so 



* A sciuare field coutaiuins oue acre is 203 feet and a few inches on each side. 



