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THE FARMER'S MAGAZINE. 



operate in the process of vegetation. It is probable 

 that we are yet unacquainted with any of the true 

 elements of matter ; for general substances, that were 

 formerly thought simple, have been decompounded, and 

 the most recent discoveries are by no means sufficient to 

 penetrate into the deep mysteries of organized life, and 

 it is doubtful if the propagation of vegetables has been 

 in any degree rendered more intelligible or easier of 

 comprehension. The original vegetables — lichens and 

 mosses — that grew on the naked decomposing rock, 

 could have little other food than water and atmospheric 

 air ; and, though chemists yet regard carbon as a simple 

 and uncompounded substance, and have found it in 

 water and in air only in a very minute degree, but by 

 some supposed to be decomposible, we may very reason- 

 ably think that water and air are the chief ingredients 

 of the food of plants; and, if the conclusion be true, it 

 is more curious in speculation than in practice, for it is 

 certain that no plants can be raised to perfection with- 

 out the aid of vegetable mould. Plants growing in a 

 rich soil must derive nourishment from it in some way; 

 for if removed to one less fertile, they decay, and often 

 die quickly. Sap is ascending and descending ; rises in 

 the spring to the leaves, where it is elaborated, and under- 

 goes some change, and descends to every part of theplant, 

 becomes a part of the substance, and adds to the bulk. 

 Sap is also changed at the first entrance by the vessels 

 of the roots ; for ingrafted plants can derive from the 

 common stock the sap peculiar to itself. But what that 

 sap, or food, or substance is, we have not been able to 

 discover, owing to the minuteness of the rootlets, fibres, 

 tubes, and pores, which almost escape detection by the 

 microscope ; and it may be very reasonably presumed to 

 be in a state of solution as it ascends the organs in a 

 liquid form. But in what way, or by what peculiar 

 operation, tl.e soil and manures yield the food in a liquid, 

 or in any other form, and become so highly conducive 

 to the growth of plants, is a point of very difficult re- 

 search, and all the conclusions yet formed on the subject 

 must be regarded as matters of very doubtful specula- 

 tion. Fortunately, the importance of being known 

 seems much less than the difficulty of obtaining the 

 knowledge ; for, if we were in possession of the latter 

 as amply as could be wished, it is doubtful if any useful 

 result would be derived, or if it would not rather re- 

 main a part of the ostentation of science, containing 

 most beautiful scientific truths, but totally irreducible 

 to practice. 



In the present generally received opinion of the aclion 

 of manures, it is supposed they exert an influence in 

 several ways — in imparting the matters they contain 

 that are favourable to the growth of plants, and also by 

 adding by future decomposition to the quantity of vege- 

 table matter already in the soil, and thereby increasing 

 the fertility by operating upon other matters in the soil, 

 breaking the texture, and setting at liberty other in- 

 gredients, and forming new combinations favourable to 

 the growth of vegetable life, and by producing clianges 

 and alterations in tlie constitution of the soil, and 

 bringing it into a more proper condition for yielding 

 food to plants, and also by acting partly in all the dif- 



ferent ways now mentioned. Thus, it may be said that 

 some manures afford nourishment only; others yield 

 nourishment, and, by leaving an earthy residue, add to 

 the bulk of the soil ; and others, again, do not nourish 

 in their own nature, but exert an agency on other sub- 

 stances, and convert them into food for plants ; and 

 there is probably no manure that does not operate in 

 more ways than one. These supposed modes of opera- 

 tion are resolved into the mechanical and chemical 

 agency of manures : the first, by reducing the texture, 

 dividing the earthy particles, and rendering the soil more 

 open and porous, and in other cases more firm and com- 

 pact, and adding to it by decomposition ; and the second 

 operates by the chemical attraction and affinities which 

 different ingredients brought into contact exert on each 

 other and on the soil, forming new combinations, and 

 producing atiriform or elastic fluids by means of the heat 

 generated in the soil during the operation of the chemical 

 combinations — thus joining with the mechanical agency 

 in producing a state of action highly conducive to the 

 growth of plants. 



The decrease in the quantity of produce on land by 

 the ceasing of the action of manures may be accounted 

 for by the chemical affinities having exhausted their 

 activity, and every particle of the earth being at rest, 

 and no more heat being generated to produce the elastic 

 fluids. And as experience has ever shown that 

 the benefits derived from the use of manures are 

 generally in a direct ratio with the quantity 

 applied, and with the character of the upper soil with 

 respect to quality and depth, it may be concluded that 

 the sujieriority of manures in the latter case arises from 

 the greater quantities of each substance affording a 

 greater number of affinities and combinations that pro- 

 mote the growth of plants. And experience has also 

 taught that if manures of any kind be applied to any 

 subsoil prepared as the upper soil generally is, no such 

 fertilizing effects will ensue ; that subsoils differ in 

 quality, and that some are very pernicious to vegetation, 

 and require long exposure, working, and manuring to 

 dispel the noxious qualities. And it may be inferred that 

 the failure in the action of the manures arises from tlie 

 substances brought into contact having less chemical 

 affinity, and consequently not forming the combinations 

 that are necessary for the growth of plants, and that the 

 upper stratum, or cultivable soil, has undergone a long 

 series of preparations, which has fitted it for entering 

 into immediate action with the manures applied to fur- 

 nish food for vegetables ; and the mode of that prepara- 

 tion may never he known. The action of manures, and 

 the benefits derived from them, are much aflected and 

 modified by local circumstances and external agencies, 

 and by a soil too wet or too dry, and by a climate being 

 too dry or loo humid ; and as similar constitutional 

 qualities in soils are rendered very different by tlie.«e 

 causes, many cases will find that manures are similarly 

 affected, and give proportional results. 



It seems evident that organic matter furnishes food 

 for plants ; and recent chemical analysis has found the 

 impoverishing effects inflicted on soils by cropping to 

 consist in a diminution of that substance, and not of 



