MANURES. 57 



converted into food for a new race, thus linkingthe whole creation 

 together in an unbroken chain. 



But another branch of the subject yet remains to be considered. 

 We have seen that plants contain but a small proportion of min- 

 eral or inorganic matter. The organic substances on the other 

 hand are by far the most abundant. They compose the great bulk 

 of the plant, constituting generally more than ninety per cent of it, 

 although they are few in number, and three out of four of them, 

 when pure, being always found in the form of gas. They are 

 oxygen, hydrogen, nitrogen and carbon. Unlike the inorganic 

 matter, these are not derived solely from the earth. Indeed, it is 

 a point not yet settled whether some of them are not derived ex- 

 clusively from the atmosphere. That there is a sufficient amount 

 in the atmosphere to furnish plants with all they require, may be 

 true, and yet at the same time it may not be true that they receive 

 them all from this source. If it be true, then a great error has 

 existed, and still exists, and is increasing in extent under the au- 

 thority of science, in the preparation of farm-yard manures and 

 composts for application to the soil. Instead of preventing tho- 

 rough decomposition in the dung-heap, or checking it when it has 

 reached a certain point — instead of using gypsum or charcoal to 

 arrest the gases as they escape from decomposing animal matter — 

 instead of ploughing in green manures or adding any vegetable or 

 animal matters to the land, the proper course would be to decom- 

 pose all such substances as perfectly as possible, or actually burn 

 them, thus suffering all the volatile parts to escape into the atmos- 

 phere, whilst the ashes alone are retained to be applied to the soil. 

 Liebig himself, to whom this whole theory is often imputed, says, 

 that humus is of use in the soil as a source of carbonic acid to 

 enable the plant to gain time, that is, to increase rapidily ingrowth 

 in a short period ; thus admitting that this gas is derived from the 

 soil in part, while he adds, that by this means " space is obtained 

 for the assimilation of {he elements of the soil necessary for the 

 formation of new leaves and branches ; meaning the inorganic 

 substances." — {Familiar Letters on Chemistry, Letter 15th.) 



But the experiments of Saussure seem to show, that the plant 

 may not only derive its carbon from the soil in the form of carbonic 

 acid, but that it has also the power of absorbing it in other forms 

 and assimilating it. Practically considered, safety lies on the side 



VOL. I. NO. 1. H 



