CHAPTER XIX 



ABSORPTION OF NUTRITIVE SALTS BY 

 AGRICULTURAL PLANTS 



All the salts taken up by the roots of agricultural 

 plants are in solution when absorbed. The movement 

 into the root thus depends on the presence of moisture, 

 which is the medium of transfer. The root-hairs are the 

 great absorbing organs of the plant, and through the 

 cells of their delicate tissues the solutions of the various 

 salts are passed. 



319. How plants absorb nutrients. — The nature and 

 quantity of material absorbed by a plant is determined 

 by the law of diffusion. From the cells of the root-hairs 

 the dissolved salts are transferred to other parts of the 

 plant, where they undergo the metabolic processes that 

 determine which constituents shall be retained in the 

 tissues of the plant. The unused ions that remain in 

 the plant juices prevent by their presence the further 

 absorption of those particular substances from the soil 

 water. It thus happens that the composition of the 

 ash of a plant may be very different from that of the 

 substances presented to it in solution. For example, 

 aluminium, although always present in the soil in a very 

 slightly soluble form, is present in mere traces in the ash 

 of most plants. On the other hand, iodine, although 

 present in sea water only in the most minute quantities, 

 is present in large quantities in the ash of certain marine 

 algse. 



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