SOILS AND FERTILIZERS. 371 



part of the ash constituents takes place during early growth and be- 

 full development of the root, system a much larger amount of soluble 

 plant-food must be present in the soil than merely suffices for a single 

 crop, because it has to be where the roots are, and these have not 

 penetrated yet and spread through the whole mass of cultivated soil. 

 The food must seek the roots rather than the roots the food, and stint- 

 ing the plant at this early stage of growth is fatal to its full develop- 

 ment and a sure way to a short crop. Abundance of plant-food at the 

 beginning is prudent husbandry at the end — a truth which becomes 

 plainer yet when we examine the mechanism of root absorption. 



The soluble plant-food, which we have called available, forms no 

 real solution, in fact, as the term solution is usually understood. To be 

 sure, we can grow plants in water alone, but to do so requires unusual 

 skill and constant attention to a multitude of minor details, which ren- 

 ders the growing in this manner of our cultivated plants a practical 

 impossibility. All such plants require air in the soil as well as above 

 it, and would speedily perish if their roots remained for any length of 

 time in a water-logged medium, be this filled with water alone or a so- 

 lution of plant-food of the proper concentration. The nutritive solu. 

 tion, which is meant whenever the name is used in this connection, is a 

 solution of about one part of nutritive substance in a thousand parts 

 of water, moistening every particle of earth with a film of liquid ready 

 to be sucked up by the tender roots of the plant as soon as they touch 

 it, but yet leaving the earth as a whole moist, it is true, but filled with 

 abundance of circulating air, and certainly free from any visible or run- 

 ning water. With such a solution and under such conditions, absorp- 

 tion, assimilation and growth occurs — vigorous, normal and healthy 

 growth. That such such growth implies also greater power to resist 

 disease and recover from injury is to be presumed, and represents a 

 quality in the plants of our crops which, in the light of tremendous 

 losses from fungus diseases and depredations of insects, cannot be 

 valued too highly. On the other hand we must suppose, however, that 

 plants may imbibe, at times, greater quantities of mineral matters than 

 they actually need for their development, just as animals often swallow 

 amounts of food much in excess of their necessities; but the waste is 

 difficult to prevent in both instances, and especially difficult in the case 

 of plants. And what now are the quantities of plant food that are re- 

 quired by our crops? An examination of their weight and composi- 

 tion will give the desired information. 



THE CROPS. 



In discussing the quantities of mineral matter that are removed by 

 our crops from the soil, it would lead too far here to consider all the 



