Recent Publications on Manures. 85 



reason for believing, when we come to what Dr. Madden says on 

 the subject, that humus does ultimately form great part of the 

 food of plants. " Trees," Dr. Madden says, " derive most of 

 their fluid nourishment from the soil, though some kinds can, no 

 doubt, get what they need by the leaves, if this source is stopped." 

 The roots, he thinks, cannot absorb gases as such, but only in 

 solution in water. " The quantity of organic substances buried 

 in the soil undoubtedly increases production," he says, "as crops 

 are always heaviest near towns. It displays the wisdom of Pro- 

 vidence, that consumption itself should increase the article con- 

 sumed. All who write on the function of nutrition are in fault", 

 he thinks, " as they speak only of the elements of the food, and 

 not of the form the elements are presented in. The physician," 

 he says, "knows that all meat consists of the same ultimate 

 elements, but he reckons one kind of food more conducive to 

 health than another. Different kinds of soil," he says, "accord- 

 ing to their nature, will modify food differently ; as one kind of 

 soil fits wheat best, another turnips." Different results will also 

 be found from different soils, according to the dampness or 

 warmth of the climate, and according as these vary in different 

 seasons. Crops of certain kinds will flourish on dry sandy soils 

 in a wet season ; while, in a dry season, they would succeed 

 better on a retentive clay. Even different degrees of pulveris- 

 ation suit different seasons best, and agriculture may come ulti- 

 mately to depend much on meteorology, were it once made more 

 certain in its conclusions. Every practical man knows, when he 

 sets about the sowing of a great breadth of ground in small seeds, 

 of how much benefit it would be to know whether dry or wet 

 weather is to succeed. If the weather is to be dry, he should 

 rake fine, and cover deep ; if wet, the deep covering will be too 

 weighty, and the finely raked soil will skin on the top, and, in 

 some instances, cause the loss of the whole crop. The palate of 

 animals gives the relish for the different kinds of food; the 

 nervous system of animals gives them, in this respect, an advan- 

 tage over plants, and, requiring more constituents, they require 

 greater variety in food. We cannot say yet that the spongioles 

 of plants come near to the sensitive perceptions of animals, but 

 they may approach nearer than we imagine, and it is not always 

 the most highly relished food that is beneficial. It is also a fa- 

 vourite doctrine of those who contend that the air is the sole 

 source of nourishment to plants, that organised substances cannot 

 be absorbed and assimilated, till decomposed into their gaseous 

 elements. I noticed before, in my former essay, that it is 

 found that starch, sugar, and gum are laid up as the food of 

 germs and buds in plants in the autumn, and again taken up 

 and decomposed in the plant itself in spring, and become part of 

 the circulating fluid, latex, or blood of the plant, to give off their 



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