RECAPITULATION. 29 



5. The importance of organic matter in the soil, is sustained by many well established 

 facts : 



a. In the removal of crops of beans, wheat, indian corn, etc., the soil is exhausted of 



not only inorganic but organic matter ; and in order to restore fertilit)'^, experience 

 proves the necessity of adding nitrogenous matters. The most striking results flow 

 from those manures which contain the most organic matter already prepared for 

 the uses of the plant, such as guano and night soil ; and in the application of these 

 substances, we become aware of tlie value of their presence in the soil. Ashes, 

 which is usually regarded as a manure wholly inorganic, is really complex, and 

 contains much organic matter. Organic matter in fact adheres so obstinately 

 with phosphoric salts, as well as the alkalies, that no form of matter which is 

 applied to land as a fertilizer is entirely free from it. If there are any exceptions, 

 it is in the use of lime of the oldest rock, and in pure gypsum. 



b. It is well established that one of the conditions necessary to secure the favorable 



action of lime, is the presence of organic matter. It is not sufficient that there be 

 carbonic acid in the atmosphere, or ammonia : it is necessary that it should exist 

 there in the condition of a product undergoing decay, by which the oxygenized 

 products may be acted upon, and by which the peculiar organic acids may be 

 produced. 



c. In regard to the entrance of nutriment into a plant, I can not but regard the root 



as its channel. Experience upholds the idea at least ; and though the leaf has 

 the power of absorbing carbonic acid and ammonia, yet it is really analogous to 

 the power of the skin also to absorb matters : still it is not the function of the skin 

 to supply food to the system. Vicarious functions are quite different from natural 

 ones. Hence the argument that organic matter in the soil could not furnish 

 enough for the wood produced in a forest, does not prove that the forest received 

 its increase through the channels of the leaves. The ammonia and carbonic acid 

 failing with the rains to the earth, supply additions of nutriment to the soil. 

 Again, it is not enough that the inorganic manures be employed. Experience 

 proves that their good effect on crops fails in due time : indeed, perfect seed can 

 not be produced in their absence. All essential and perceptible increase of pro- 

 ducts comes from manuring, and in proportion to the manure ; and trees or shrubs 

 whose branches are cut off from the supply below, die, not from the absence of 

 water alone, but from starvation : they can maintain but a precarious existence 

 under the most favorable circumstances. 



d. The quantity of carbonic acid is about one-thousandth of the weight of the 



atmosphere. This is sufficient, no doubt, to preserve, so far as this is concerned, 

 the balance of nature. Being produced by the respiration of animals and by 

 combustion, and diffused through the atmosphere, it is again brought to the soil. 

 So it is produced in vast quantities in the soil by slow combustion, and manures 

 must yield the same product in the very place where it is particularlj' wanted. 



