EEMOVAL OF NUTRIENTS FROM THE SOIL 291 



Bouyoucos 1 has suggested that the phenomena of wilting may 

 be due, at least partially, to plasmolysis since he has shown 

 by observing the depression of the freezing point that the soil 

 solution becomes very concentrated at low moisture contents. 



Such a conception of water absorption is simple, yet it often 

 leads to erroneous ideas regarding the intake of nutrients by 

 plants. The amount of any particular nutrient absorbed by 

 the plant is not determined by the quantity of water taken up, 

 since water and nutrients enter more or less independently. 

 The large amount of water imbibed by the plant, later to be 

 lost by transpiration, cannot be accounted for on the basis of 

 a very dilute soil solution and the necessity of rapid trans- 

 piration in order to facilitate the entrance of sufficient nutrient 

 substance. 



153. Absorption of nutrients by plants — diffusion. — The 

 solution in a normal fertile soil is not only rather dilute 

 in toto but a great proportion of the nutrients therein are in 

 the ionic condition. While both molecules and ions are pre- 

 sented to the absorbing surfaces of the plant, it is only the 

 latter that penetrate to any great extent, although some mate- 

 rials, especially those of an organic nature, do enter in a 

 molecular condition. The presence of water is, of course, nec- 

 essary for both ionic and molecular penetration, but only as a 

 medium for diffusion. Its movement into the plant is, there- 

 fore, of no very great moment in the actual diffusion process, 

 as the phenomenon is called, although the approach of the 

 nutrients to the feeding surfaces is considerably influenced by 

 capillary activity. 



The tendency of diffusion is to equalize the concentration 

 of a solution as to the ions and molecules of its solute, the 

 molecules and ions of different salts moving more or less inde- 



loss of water. It is a shrinkage of the protoplasm and when carried 

 beyond a certain point permanently injures the cell. 



1 Bouyoucos, G. J., The Freezing Point Method as a New Means of 

 Measuring the Concentration of the Soil Solution Directly in the Soil; 

 Mich. Agr. Exp. Sta., Tech. Bui. 24, 1915. 



