86 Recent Publications on Manures. 



constituents to the different organs as required by the necessities 

 of each. The same substances, when in solution, must therefore 

 be the food of plants. The gum and sugar have been reckoned 

 organisable, not organised, products ; starch, however, is ad- 

 mitted to be more highly organised ; and lignin, the most highly 

 organised of the abundant products of plants, can be reduced to 

 the others by simple chemical processes : there is abundant 

 proof to establish that the vital chemistry of the plant itself far 

 exceeds what can yet be imitated. Sir Humphry Davy exhi- 

 bited starch, jelly, and other highly organised products to plants, 

 and found they formed food. In an essay of Professor Gazzin 

 of Italy, an eminent chemist, and formerly a pupil of Sir Hum- 

 phry Davy (as translated by Mr. Crawfurd of Auchindrames, 

 and read to the Ayrshire Agricultural Association, and after- 

 wards published in the Ayr Advertiser), it is stated, "that if we 

 dilute a quantity of nearly rotten farm-yard manure in water, 

 and pass it through a coarse sieve, a great deal of straw and 

 undecomposed organic matter is retained ; if we pass the 

 liquid again through a closer sieve, straiter in the meshes, we 

 will find still smaller pieces of undecomposed, brown-coloured, 

 organic substances; still smaller pieces will be got from a still 

 straiter sieve; and so on, till we come to pieces," he says, " that 

 are undoubtedly soluble in water, and form the food of plants. 

 Great waste of manure," he thinks, "is thus made by decompo- 

 sition, and he would have the straw cut and bruised, and depo- 

 sited in the ground, to decompose there." We see from the 

 above-quoted opinions of the learned professor, good ground for 

 believing that soluble organic substances are, indeed, part of the 

 food of plants. It may be matter of doubt whether the straw 

 would not be broken down and become soluble more easily in 

 the dung-heap : small quantities in the soil do not ferment so 

 l'eadily, and care being used to preserve as much as possible of 

 the products of fermentation, most practical men seem to be in 

 favour of rotting the dung. On this subject I entered at great 

 length in my former essay, which supersedes the necessity of 

 bringing it again forward. As corroborative of the great benefits 

 of manure exhibited in a soluble, or nearly soluble, state, I 

 may notice the great effects of brewers' grains spread on a field 

 in Glamorganshire, which produced four times the quantity 

 usually got from the same soil. Professor Johnston, on the 

 same subject, says, " when we see red-coloured substances 

 absorbed by the hyacinth roots, from the water iu which they 

 are growing, and colouring the white flower, till again dis- 

 pelled by the elaboration of the petal, which returns to its 

 white colour as before; we cannot divest ourselves of the 

 belief, that all organic substances soluble in water are ab- 

 sorbed by the roots, and elaborated in the leaf." On the ques- 

 tion whether all the carbon of plants is got from the air, he 



