94 , THE SOIL. 



Absorption of nutriment from the soil is effected by 

 the extremities of the roots, whose fluid contents are 

 separated from the earthy particles around them by an 

 exceedingly thin membrane alone ; and the contact of 

 the two is the more intimate, as the root-fibre during 

 its formation exerts upon the earthy particles a pres- 

 sure sufficiently powerful, under certain circumstances, 

 to push them aside. The evaporation of water from the 

 leaves produces a vacuum within the plant, whereby a 

 draught is created, which powerfully assists the con- 

 tact of the moist earthy particles with the cell-wall. 

 The cell and the earth are pressed against each other. 

 Between the fluid contents of the cells and the nutritive 

 substances physically combined in the earthy particles, 

 there manifestly exists a strong chemical attraction, 

 which, with the cooperation of carbonic acid and water, 

 causes the transference of the incombustible matters 

 into the system of the plant. 



By the powerful chemical attraction of any body, 

 we understand its entering into a chemical combination, 

 in which it loses its original properties and acquires 

 new ones. In the case of potash, lime, and phosphoric 

 acid, such a combination must take place immediately 

 upoii their passage into the cell ; for, as already stated, 

 the sap of the roots is always slightly acid. In. the sap 

 of the root-shoots of the vine, we can always detect 

 bitartrate of potash ; in that of others, oxalate or citrate 

 of potash, or tartrate of lime ; but we never find these 

 bases combined in such saps with carbonic acid, nor 

 can phosphate of lime or magnesia be detected. If the 

 fresh sap of the potato-tuber is mixed with ammonia, 

 no precipitate of phosphate of magnesia and ammonia 

 is produced ; but this precipitate makes its appearance 

 as soon as the fermentation of the sap has destroyed 

 the (azotised) substance with which the phosphate of 

 magnesia is combined. 



Careful mixture and distribution of the nutritive 

 substances present in the soil, are the most important 

 means of rendering them effective. 



A piece of bone, weighing half an ounce, placed in 



