18 Nebraska Agricultural Exp. Station, Research Bui. 6. 
soil solution under conditions of high evaporation rate. The 
density of the soil solution as taken into the plant is not neces- 
sarily the same as the density of the soil solution as it exists within 
the soil. The transpiration rate may be independent of the 
density of the soil solution as it exists within the soil or as taken 
into the plant. The evidence in no way corroborates the theory 
that the necessity for or the rate of transpiration may be reg- 
ulated thru the density of soil solution. 
29. Considerable variation existed between the different 
varieties of corn and sorghum in regard to the thickness of the 
leaf and of the epidermis and also in the number of stomata per 
unit of leaf-area. There was, however, no apparent striking or 
consistent correlation between these histological coefficients and 
the transpiration rate per unit of dry matter or per unit of leaf- 
area of the different varieties. There was also no striking re- 
sponse in the relative number of stomata to variation in either 
soil moisture or soil fertility. 
30. As an average for 11 varieties of corn, a plant having 
949 square inches of leaf-area had 104,057,850 leaf stomata. 
The stomatal apertures in the epidermis of both sides of the leaf 
occupied, when open, 1.52 per cent of the entire area of the leaves. 
The stomata were found to be practically closed at night and also 
when the leaves are wilted. The entire epidermis comprised 30.8 
per cent of the leaf thickness. 
31. Many of the factors influencing the economy of water use 
by plants, which have been commonly regarded as directly in- 
fluencing the transpiration rate as such, are rather factors in 
plant nutrition. Any factors which cause malnutrition result in 
a relatively high water requirement in the production of dry 
matter, because of the continued use of water without a normal 
increase in dry matter. 
Transpiration appears to be a purely physical phenomenon, 
depending primarily upon the moisture supply in the leaf and the 
evaporating power of the atmosphere, which is modified in some 
degree by temperature effects resultant within the leaf from 
chemical activity, transpiration, and from the absorption of 
radiant energy. 
