ABSOEPTION OF NUTRITIVE SALTS 406 



A plant will, in general, take up more of a nutritive 

 substance if it is presented in large amount, as compared 

 with the other soluble substances in the nutrient solution, 

 than if it is presented in small amount. Thus, the per- 

 centage of nitrogen in maize, oats, and w^heat may be 

 increased by increasing the ratio of nitrogen to other 

 nutritive substances in the nutrient media. This is 

 also true of potassium and phosphorus, respectively. 

 This fact is accounted for by the maintenance of the 

 osmotic equilibrium at a higher level for a particular 

 ion which is relatively abundant in the nutrient solution, 

 thus preventing the return of the excess from the plant, 



320. Relation between root-hairs and soil particles. — 

 In a rich, moist soil the number of root-hairs is very 

 great, while in a poor or a very dry soil or in a saturated 

 soil there are comparatively few root-hairs. The con- 

 nection between the root-hairs and the soil particles is 

 extremely intimate. When in contact with a particle 

 of soil, a root-hair in many cases almost incloses it, and 

 by means of its mucilaginous wall forms a contact so close 

 as practically to make the solution between the particle 

 and the cell wall distinct from that between the soil 

 particles themselves. 



There has been considerable difference of opinion as to 

 how a plant can obtain its mineral nutrients from a sub- 

 stance so difficultly soluble as the soil. This has arisen 

 because of the conflicting nature and the inadequate 

 character of the data available. 



321. Liebig and Sachs on • solvent action of plant 

 roots. — Liebig ^ called attention to the fact that a plant 

 may obtain one hundred times as much phosphorus and 



1 Liebig, J. Die Chemie in Ihrer Anwendung auf Agrikultur. 

 1862. 



