246 The Ohio Naturalist. [Vol. XIV, No. 4, 



some cases an insufficiency of any salt will operate as a limiting 

 factor, the plants continue to transpire and yet make little growth, 

 or may even show a loss in weight accompanied by a high trans- 

 piration; in other cases the conditions retard or inhibit growth 

 as well as transpiration and produce the effect of ph^-siological 

 •drought; still other cases exhibit no detrimental effect, but rather 

 an increase in growth and in yield of plant material with little 

 or no change of transpiration ; stimulation may accelerate or 

 diminish the rate of transpiration, but not necessarily that of 

 metabolism or growth. These phenomena have been shown 

 repeatedly by the work in this laboratory (Bull. 16, 1912, Geologi- 

 cal vSurvey of Ohio) and by the experimentation of various investi- 

 gators elsewhere. 



Variation in green and dry weight of plants and a great 

 expenditure of energy often indicated by a loss in total weight, 

 commonly occur during activity in spring while leaves are unfold- 

 ing; the inequalities cannot be attributed to differences in rate 

 or amount of transpiration. The greater absorption and dis- 

 tribution of mineral salts and organic material which has been 

 reported under conditions of increased humidity, of shade, or 

 at different periods of growth is not detemiined by an accelerating 

 effect of the transpiration current. In autumn, following the 

 death of leaves, when there is a relatively rapid migration of 

 mineral and organic substances to other parts of the plant, it 

 becomes obvious that the transpiration stream is not the medium 

 by means of which a plant can obtain a better supply of the 

 necessary nutrients. The translocation of organic or inorganic 

 material to leaves, or from storage regions to places where they 

 are used up, is a phenomenon of wide occurrence in aquatic 

 plants, in underground parts of land plants, in plants occupying 

 very humid and very dry land areas. Maximum growth is 

 correlated with a large movement of materials, but the more 

 vigorous translocation and absorption of salts and organic material 

 can rarely be referred to a greater transpirational water loss 

 or to a more vigorous transpiration current; the rate and the direc- 

 tion of the movement of the solutes and water is independent 

 of one another. The causes of these phenomena are identical 

 with those recorded for the selective absorption of roots. They 

 are conditioned by the differential permeability of the proto- 

 plasmic membranes of cells, and arc related and dej^endcnt upon 

 the more complex metabolic influences of the entire organism. 

 One can comprehend the advantage which plants with woody 

 tissue have over those in which the movement is wholly in the 

 cortex, but the reasons advanced in .support of the transpiration 

 view do not appear quite sound. A number of plants show 

 "preferences" for lime soils in one part of their areal range 

 Avhich are not typical in another habitat. Others thrive, 



