108 



THE SOIL. 



"Water stagnant in the ground, so far from promot- 

 ing the absorption of food, injures the growth of land- 

 plants. 



If plants really did receive the elements of their 

 food from a solution which could change its place in 

 the soil, then all drainage waters, spring, brook, and 

 river waters, must contain the principal nutritive sub- 

 stances of all plants ; and it must be 'quite practicable, 

 by continued lixiviation, to extract from every arable 

 soil, without distinction, all the nutritive substances, 

 either entirely, or at least in amount corresponding to 

 the quantity contained in a crop. But, in reality, this 

 is not practicable. By the action of water, the field 

 loses none of the principal conditions of its fertility, in 

 such a degree as perceptibly to impair the growth of 

 plants cultivated on it. 



For thousands of years, all fields have been exposed 

 to the lixiviating action of rain-water, without losing 

 their powers of fertility. In all parts of the earth, 

 where man for the first time draws furrows with the 

 plough, he finds the arable crust, or top layer of the 

 field, richer and more fertile than the subsoil. The fer- 

 tility of the ground is not diminished by plants grow- 

 ing thereon ; not until the plants are removed from the 

 ground does it gradually lose its fruitfulness. 



The opinion that some cause is at work within the 

 plant itself, which seems to render soluble certain ele- 

 ments of food, and make them available for nutrition, is 

 not contradicted by the experiments of Knop, Sachs, 

 and STOHMANN, who have shown that many land-plants, 

 without touching a particle of earth, may be brought 

 to flowering and seed-bearing in water, to which the 

 mineral elements of food have been added. These ex- 

 periments, which have thrown considerable light upon 

 the physiological importance of the several nutritive 

 substances (see Appendix E.), merely prove how ad- 

 mirably the ground is adapted to the requirements of 

 plants, and how much human ingenuity, knowledge, 

 and minute care, it takes to supply, under circum- 

 stances differing so widely from the natural condition, 



