Amount of Water Used by Plants 41 



1892, 19 inches gave 8,189 pounds, leaving the rate of evapo- 

 ration from the plant surface very nearly the same for the two 

 seasons, in spite of the differences of humidity and of wind 

 velocities. 



In the case of barley for these two years, there was a wide 

 difference in the amount of water used per unit area, 13.19. inches 

 being used in 1891 and 23.52 inches in 1892. But the yields of dry 

 matter per unit area were also widely different, being 7,441 pounds 

 of dry matter per acre in 1891 and 14,196 pounds in 1892. The 

 barley in 1891 used 3.54 inches of water per ton of dry matter, 

 and in 1892, 3.31, or only .23 inches less, which is small. 



Even when the conditions are as different as those in the 

 plant-house and the open field, the differences are not as marked 

 as we were led to expect, as the table which follows will show: 



-In field . ; In plant-hous< 



Acre-inches of water Acre-inches of water 



No. of trials per ton of dry matter No. of trials per ton of dry matter 



Maize.... 8 2.433 44 2.386 



Oats 8 5.011 12 4.535 



Clover... 24 5.345 22 5.005 



Total 40 Mean 4.263 Total 78 Mean 3.975 



If the results are expressed in pounds of water used per 

 pound of dry matter, then they stand as follows : 



Pounds of water per Pounds of water per 



No. of trials pound of dry matter No. of trials pound of dry matter 



Maize.... 8 275.6 44 270.3 



Oats 8 567.8 12 490.6 



Clover... 24 605.5 22 567.1 



Total 40 Mean 483 Total 78 Mean 442.3 



The tables show that in the case of these crops maize, oats 

 and clover they have used in the field .288 acre -inches of water 

 more per ton of dry matter produced than in the plant -house ; or, 

 when expressed in the other way, 40.7 pounds of water per pound 

 of dry matter more in the field cylinders than in the cylinders in 

 the plant-house. Expressed in percentages, the field conditions 

 demanded 9.2 per cent more water when the cylinders stood out- 



