30 



RECAPITULATION. 



Must we suppose that the carbonic acid thus derived from the decay of vegetables, 

 and from the manures added, is evolved in a gaseous state, and ascends to the 

 leaves for absorption 1 This will not gain credence. 

 e. So of ammonia : this must be continually supplied. The original store of it, which 

 may be supposed, for argument, to have been thrown into the atmosphere, would 

 long ere this have been exhausted. It must be reproduced, and it is well known 

 to be reproduced in the decay of vegetables, and also that a part is resolved into 

 nitrogen and hydrogen. The decompositions in the soil become a source of 

 ammonia : this need not escape into the atmosphere for the absorption of leaves. 

 Manures, too, furnish it during their changes in the soil ; and it is not probable 

 that it must leave the soil in order to reach the vegetable tissue. 



f. If, however, manure is left uncovered, will the crop get the benefit of it? Here 



it goes into the atmosphere; but who will maintain that the field will yield the 

 crop it would, had it been covered and well mixed with the soil 1 When am- 

 monia is fixed by ground gypsum, is not the conclusion evident that it reaches 

 the leaves of plants through the root? 



g. The soil must possess all the inorganic substances, as well as organic, which are 



essential to the perfection of vegetables : if any one is wanting, it must be sup- 

 plied. But to secure its benefits in the highest degree, the soil must be put into 

 a state which shall make all those matters accessible to the roots of plants. This 

 calls for the attention of the husbandman to its mechanical condition. 

 h. It is maintained that certain crops, as clover, take nitrogen from the air. May it 

 not be doubted, and may not the advantages to be derived from its cultivation 

 arise from its large and widely branching roots, whereby a rapid growth is secured 

 by an absorption of nitrogenous matters from comparatively large areas. 

 Modern chemists and physiologists have established the doctrine, that the vegetable 

 kingdom is the great source of nourishment to the animal kingdom. In the vegetable 

 kingdom, albumen, fibrin and casein, substances essential to the maintenance of 

 animal life, are elaborated. So both kingdoms yield back the inorganic matters to 

 the mineral in their decay, and combustion and respiration are other means by which 

 the food of plants is in part prepared. It will suggest itself to the reader, probably, 

 that the actions of the vegetable end in results totally different from those of com- 

 bustion and respiration. In the leaf, oxygen is set free; in combustion, it is fixed. 

 Oxygen and carbon being united in animal life, it becomes the part of the vegetable 

 to separate them ; to appropriate the carbon in the growth of wood, while at the same 

 time oxygen is once more in a condition to meet the wants of animals. 

 It is impossible to overlook, in these changes, the balance which is preserved by the 

 controlling agencies of nature. Mutual adaptations prevail : harmony is secured. 

 To the vegetable is allotted the task of elaborating the fluids most essential to the 

 growth of animals. The vegetable has time and leisure to do this. To say that the 

 plant ven-ptatos. is (o express the whole of its life and doings. 



