BOOTS AND THBIK FUNCTIONS. 47 



some well-supported facts, for rejecting them. It is cer- 

 taialj consistent with the almost universal observation of 

 practical as well as scientific cultivators of plants, that 

 soil containing organic or vegetable matter is far more 

 productive than that from which it is wholly absent. It 

 is true that some kinds of plants will grow in a soil con- 

 taining no perceptible amount of vegetable matter, yet 

 we all know how much more luxuriantly plants will grow 

 in the presence of an abundance of decomposed or decom- 

 posing carbonaceous materials. The fact, however, 

 should not be overlooked, that in the decomposition of 

 vegetable matter^ other elements are set free in addition 

 to carbonic acid, and it is not readily determined as to 

 which one among the number contributes most to the 

 increased fertility of the soU. 



Every intelligent cultivator of plants knows that as 

 each crop is taken from the land, its fertility ii lessened, 

 owing, in part at least, to the loss of organic matter ; but 

 if each successive crop derived its entire carbon from the 

 air, and through the leaves of the plants, then it would 

 never be necessary to add anything to the soil likely to 

 yield carbon ; consequently the theory of plants deriving 

 all their carbon from the dioxide absorbed by the leaves 

 is scarcely reconcilable with what appears to be the ordi- 

 nary operations usually practised, if not positively neces- 

 sary, in the cultivation of plants. We can readily under- 

 stand, or at least believe, that it is possible, as claimed, 

 that all the carbonaceous matter now present on this 

 earth had its origin in the atmosphere ; but it does not 

 necessarily follow that each individual plant, or crop, 

 derives all, or any considerable part, of its carbon from 

 the air. 



Nitrogen is another element of plants, about the origin 

 and way in which it is utilized by plants, neither vege^ 

 table physiologists nor chemists have been able to agree. 

 Wlule some cootend tbat plants caoeQt assimilate atroos- 



