THE FARMERS' REGISTER. 



343 



of vegetable and animal euhstancee. But here 

 physiologidts and cliemisis are at real or apparent 

 variance with each other, in regard lo the anioiint 

 of carbon which plants derive from the soil. The 

 old physiologists, and some ol ihe less insirucled 

 of Ihe existing race, seeing that soils rich in 

 vegetable maiter gave generally luxuriant crops, 

 that by adding vegetable and animal manures to 

 these soils Ihey were rendered siill more produc- 

 tive, and that ihe quaniily of carbonic acid in the 

 atmosphere was so very small— have generally 

 advanced and maintained the opinion that the 

 sustenance of plams— iheir carbon— is chiefly 

 derived Irom (he soil— that what they draw from 

 the air forms but a small portion of their actual 

 substance. This opinion lias been suijected by 

 its defenders to sirange tvvistings and stretchings, 

 to account (or such facts as ihese. A field almost 

 desliiute of vegetable matter is laid down lo 

 grass, when year by year, though depastured all 

 ihe while, the vegeiable matter increases, till at 

 length lour or six inches of rich, dark, vegetable 

 mould are Ibrmed upon iis surface. 6r a waste 

 is planted with trees, which every succeeding 

 autumn shed their leaves on the surlijce, and 

 though much is carried off in thinnings, and the 

 entire /brest is sent to market when the irees are 

 of sufficient size, yet the soil contains more vege- 

 table matter at the end of all this, than it did'^at 

 the beginning. Or a tree falls across a stream, 

 dams up the water, and produces a marshy spot, 

 rushes and weeds spring up, mosses take root and 

 grow, year after year new shoots are sent forth 

 and die, vegetable matter accumulates, a bow, 

 and finally a thick bed of peat is Ibrmed. Phy- 

 siologists of the old school may doubt, but com- 

 mon sense tells us that the increase of vegetable 

 matter in all these cases— of its carbon, that is 

 --niust have been derived from the air. 



This conclusion does not imply that a given 

 plant or crop, that the individual grasses, or frees, 

 or mosses, in our three ca?es, have not each de- 

 rived a portion of their sustenance from the soil. 

 The roots of our trees, for example, are coniinu- 

 ally drawing soluble organic matter from the soil, 

 vvhich they send up to the branches and leaves. 

 But the quantity they return to it in the leaves 

 they shed, and in the roois themselves, which 

 remain buried, is something greater than what 

 they thus send up; and thus the organic matter 

 slowly increases. In our arable lands the same 

 IS shown by the slow decrease of vegetable matter 

 through prolonged culture, and the consequent 

 necessity of either adding a fresh supply of or- 

 ganic matter to maintain their fertility, or of 

 leavmg them for a lime to a process of natural 

 recovery. Still the question remains undecided 

 between the iwo parties- what portion of their 

 carbon do plants thus derive li-om the soil, and 

 what Irom the air? It appears that borage has 

 been long grown in Germany, for the purpose of 

 ploughing m as a green manure. Nearly twenty 

 years ago Lampadius, who has done much .rood 

 service to scientific agriculture, made an experi- 

 ment with the view of determining the amount ol 

 vegetable matter with which this plant was ca- 

 pable of enr,ching the soil. This experiment led 

 mm to the conclusion that borage draws no less 

 than nine-tenths of its carbon from the air. Much, 

 however, must depend upon the climate and soil ; 

 and later experiments have shown that the crops 



we usually cultivate for food derive, on an 

 average, about two-lhirds of their carbon from 

 the air, and, consequently that, if we add lo the 

 soil, in the form of manure, one-third of what we 

 take ofl^in the form ofa crop, we should maintain 

 It in lis existing stale of richness, in so far as this 

 depends upon vegetable matter, were there not 

 other causes in operation vvhich tend to lessen the 

 amount of organic matter in soils that are con- 

 tinually turned up by the plough. Our author 



thus concludes his review of this question : 



"Being thus filled by nature to draw their 

 sustenance— now li-om the eanh, now from the 

 air, and now from both, according as they can 

 most readily obtain it— plants are capable of 

 living— though rarely a robust life— at the ex- 

 pense of either. The proportion of their food 

 which they actually derive from each source, will 

 depend upon many circumstances— on the nature 

 of the plant itself— on the period of ils growth— 

 on the soil in which it is planted— on the abun- 

 dance of food presented to cither extremity— on 

 t^he warmth and moisture of the climate— on the 

 duration and intensity of the sunshine, and upon 

 other circumstances of a similar kind— so that 

 the only general law seems to be, that, like ani- 

 mals, plants have also the power of adaptin« 

 themselves to a certain extent, to the conditions in 

 which they are placed ; and of supporting life by 

 the aid ol such sustenance as may be wiihin their 

 reach. 



"Such a view of the course of nature in the 

 vegetable kingdom is consistent, I believe, with 

 all known lacts. And that the Deity has bounti- 

 fully fitted the various orders of plants— with 

 which the surface of the earth is at "once beauti- 

 fied and rendered capable of supporting animal 

 life— to draw their nourishment, in some spots 

 more from the air, in others more from the soil, is 

 only in accordance with the numerous provisions 

 we every where perceive, for the preservation and 

 coniinuance of the present condition of things." 



Another poin-t in connexion with the or'ganic 

 food of plants, and especially the source of their 

 carbon, has recently been brought into perhaps 

 unnatural prominence by Liebig, The physiolo- 

 gists, believing that plants derived from the soil by 

 lar the greatest proportion of their carbon, natur- 

 ally inquired what vegetable substances in the 

 soil entered into their roots and ministered in the 

 greatest degree to their growth. To vet^etable 

 matter, generally, they gave the name of humus, 

 and to a dark brown substance which dissolves 

 out of the soil, when it is boiled wiih a solution 

 of common soda, the name ofhumic acid was ap- 

 plied. This humic acid being olten met with in 

 considerable quantities in fertile soils, has been 

 generally mentioned by foreign agricultural writers 

 as the principal source of that portion of the 

 carbon which plants derive from the soil. It will 

 be observed that this opinion may be entertained, 

 wiihout denying, at the same time, that plants 

 derive the largest portion of their sustenance from 

 Ihe carbonic acid of the atmosphere. Liebig has 

 shown that the humic acid and its earthy^com- 

 pounds are so sparingly soluble, that, were all 

 the water which enters the roots of plants to carry 

 with it as much of them as it could hold in solu- 

 tion, it would still convey to the stem and 

 branches only a small fraction of the carbon they 

 contain. So far Liebig'a argument is unassail- 



