TH. II.] THE ROOTS. 69 



Roots then must obtain from a soil nomishmeut to 

 plants in a gaseous or liquid state : we may next, 

 therefore, consider "what constituents of soils are 

 capable of being presented in such foims. Water 

 can be the only solvent employed ; indeed, so essen- . 

 tial is this liquid itself, that no plant can exist wheiNfe/ 

 it is entirely absent ; and, on the other hand, many^ 

 will exist ^vith their roots in vessels containing 

 nothing but distilled water. Plants with a broad 

 surface of leaves as mint, beans, <tc., I have always 

 found increase in carbonaceous matter, whilst thus 

 vegetating; but onions, hyacinths, &c. with small sur- 

 faces of foliage, I, as invariably, have found to decrease 

 in solid matters. The first, at all times, obtain 

 nourishment by decomposing the carbonic acid gas of 

 the atmosphere : the latter do so in a much smaller 

 proportion: hence the reason why the latter are so 

 much more impoverishing crops than the former,' 

 inasmuch as that they acquire nearly all their solid 

 matter by means of their roots. These obsei*vations 

 explain the conflicting statements of Saussure and^^ 

 Hassenfratz on this point: the fomier experimented^ 

 with broad-leaved plants ; the latter on such as have ; 

 small foliage. The first maintained that plants in;^; 

 crease in solid content when their roots are supplied^ i 

 with water only ; the latter denied the fact. 



It has been advanced that water is the sole food of 

 plants ; but all experiments are inconclusive which 



