Feb., 1914.] 
Transpiration in Relation to Growth. 
245 
ments during the life cycle. The phenomena of selective absorp¬ 
tion show that transpiration does not determine in these cases 
the amount of salts absorbed during metabolism and growth, that 
the time of maximum absorption for different salts varies, and 
that they are absorbed at independently varying rates. Plants 
do not absorb mineral or organic constituents in the same con¬ 
centration as exists in the solution in which the roots are found. 
The data from numerous experiments show that under certain 
conditions the roots of plants remove the solutes from a solution 
faster than the water, and in a different ratio than exists in the 
solution. The process of absorption of inorganic and organic 
constituents is not connected with transpiration, but with the 
metabolism of the plant. Hence, the value of the transpiration 
ratio is, under these conditions, more frequently inversely pro¬ 
portional to the amount of growth and the luxuriance of vegeta¬ 
tion. The marked difference exhibited by different plants in 
efficiency of growth under conditions of limited water supply 
is particularly a characteristic and striking feature of variability 
in nutritive metabolism, not in transpiration. It is unnecessary 
to review such cases as include the action of mineral fertilizers— 
separately and as antagonistic or balanced solutions— the effects 
of organic compounds from peat and from mineral soils, the 
action of inorganic and organic acids and alkalies. Such investi¬ 
gations are well known. They are extremely important as they 
show that rapid production of green and dry substance of plants 
is not necessarily accompanied by a high relative or total trans¬ 
piration value. The conditions of water loss show extreme 
variations with respect to the total quantity of water available 
and required, and the amount of growth. 
Under the circumstances it is unnecessary to discuss the 
problem as to what special demands on inorganic materials 
individual plants may make, wherein the use or advantage for 
necessary essential and nonessential constituents lies, or to 
differentiate nutritive materials from those functioning otherwise. 
The specific effects produced by these substances, either externally 
or after having entered the cells and there reacting with the 
contents, differ according to the nature of the compound and if 
derived from habitat conditions characteristic of unrelated 
vegetation types, e. g., those frequenting organic soils, such as 
peat, may even interfere with growth and normal development. 
The specific physiological effects produced may be more marked 
on the roots than on the green parts of plants, or may affect 
leaf tissue more strikingly than that of the stem. These different 
reactions are due in part to modifying effects upon imbibition 
of cell colloids, largely to changes in the permeability of the 
protoplasmic membrane and in the metabolism accompanying 
the direct absorption of constituents in the soil solution. In 
