FISHERIES, GAME AND FORESTS. 429 



As shown by all the recent experiments, evaporation from the surface of plant 

 foliage is much less rapid per unit area than from water surfaces. An extended 

 discussion of why this is so is given by Kerner and Oliver in their Natural History of 

 Plants. As shown, however, by the data on page 419 the area of foliage is much 

 greater than the ground area on which the plant stands, in the case of Indian corn the 

 increase in area amounting, as a maximum, to 22.4 times the ground area. It is 

 because of this immense transpiring or evaporating surface that some plants throw off 

 more water than can be evaporated from the ground area on which they stand. 



In concluding this part of the subject the deduction may be tentatively drawn from 

 the foregoing data that hardwood forests may consume from about five to ten inches 

 in depth of water over the ground area in each growing season. Probably from six 

 to eight inches is a fair average for deciduous forests, although broad-leaved forests 

 may consume somewhat more. The most of the evergreens are small water 

 consumers, the larch being, however, an exception. Spruce and pine forests apparently 

 require only a few inches on the ground area per year. In order to insure enough we 

 may allow them from four to six inches per year. 



The figures show, therefore, that the kind of forest must be taken into account in 

 estimating the effect on yield of streams. 



As regards cultivated crops the figures show demands for about twelve to 

 fifteen to twenty inches on the ground area for cereals and grass crops. For vineyards, 

 and hop yards the tabulated figures may be increased by at least fifty per cent, to 

 cover evaporation from the naked soil between the plants, thus giving about eight to 

 eleven inches for these two agricultural crops. Everything goes to show that for grass 

 crops the consumption of water is very large, clover transpiring from 13.6 inches to 

 18.0 inches, and grass crops even more than this. As shown by the experiments of 

 Baldwin Latham, Italian ray-grass will, when given a full water supply, use up in one 

 year several times the average annual rainfall of this State. 



As a final tentative proposition we may say, therefore, that highly cultivated 

 farming areas will consume in surface evaporation and plant transpiration from two 

 to three times as much water as average deciduous forests, and from three to five 

 times as much as average evergreen forests. In mixed forests the water consumption 

 will depend upon the relative proportion of the different kind of trees. 



