32 



piration (ineXuding evaporation} is large, there is a larger 

 proportion of dry matter produced than when the trttnspiration 

 ie email. Th@ inclusion of evaporation from the surface 

 with the transpiration by some experimenters, and its 

 exclusion by others, together with different rat^a of 

 growth would be euffioient without other varying factors to 

 cause the difference observed by the investigators quoted. 



King (Wis. 8 K;ept, 126) calculated the amount of water 

 required to produce a pound of dry matter under field con- 

 ditions. Barley re^uAred 402, oats 501, a?i« corn 301 pounds 

 of water. Variations due to evaporation and capillarity 

 were included in the data. Hays (hmn, 68) calculated 

 that wheat under field conditions required 261 pounds to 

 produce a pound of dry matter. 



Warrenton (Physical Properties of Soils, 52) observes 

 that, the relation in question (between transpiration and 

 dry matter produced) appears to be fairly definite so long 

 as certain conditions remain constant, but to vary under 

 a wide range of circumstances. Further (p. 53) : "Two 

 circumstances seem especially to influence the relation of 

 water supply to produce : 



1. Til© amount of water supplied 



2. Its rie'oness or poverty in plant food. 



