Feb., 1914.] Transpiration in Relation to Growth. 245 



ments during the life cycle. The phenomena of selective absorp- 

 tion show that transpiration does not detemiine in these cases 

 the amount of salts absorbed during metabohsm 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 dift'erent 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 unnecessar\' 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 froin 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 



