PLANTS GROWN IN SOIL AND IN WATER. 109 



certain properties of arable soil, whicli insure the 

 healthy growth of plants. 



If the supply of nutritive substances in a state of 

 solution were really suited to the nature of the plant 

 and the functions of the roots, it would follow that in 

 such a solution, most abundantly provided with all the 

 elements of food in the most movable form, the plants 

 must thrive the more luxuriantly the fewer the obsta- 

 cles are which oppose their absorption of food. 



A young rye-plant, placed in a fertile soil, will 

 often send forth a bunch of thirty or forty stalks, each 

 of them bearing an ear, and will yield a thousandfold 

 crop of grains, or even more ; yet this plant draws its 

 mineral food from a volume of earth, from which the 

 most persevering lixiviation with pure water, or water 

 containing carbonic acid, will not extract even the one- 

 hundredth part of the phosphoric acid and nitrogen, 

 nor the fiftieth part of the potash and the silicic acid, 

 which the plant has drawn from the soil. How is it 

 then possible, under such circumstances, to assume that 

 water alone would have sufficed, by virtue of its solvent 

 power, to render available to the plant all the sub- 

 stances found in it \ 



None of the plants grown in watery solutions of the 

 mineral elements of their food, even though thriving 

 luxuriantly, will bear the remotest comparison, in the 

 bulk of vegetable matter produced, with plants grown 

 in a fertile soil ; and the entire process of developement 

 in them proves that the conditions of thriving growth 

 in the soil are quite of another kind. 



The greatest weight of crop obtained by Stohmann 

 from an Indian corn plant grown in water amounted to 

 84 grammes ; while he obtained from another Indian 

 corn plant grown in the soil, at the same time and from 

 the same seed, a crop weighing 346 grammes. In Knop's 

 experiments, the dry weight of two Indian corn plants, 

 the one grown in water, the other in the soil, was found 

 to be as 1 : Y. 



The water circulating in the soil contains chloride 

 of sodium, lime, and magnesia the two latter in com- 



