Chap. XIL Appendix, Paut 4. No- 2.

12.5

fruit, seeds. Certain substances added to sand and clay, areknown by experience to make plants grow more luxuriantly, somein their roots, some in their herbaceous stems and leaves, some intheir flowers, others in their fruit, and others in their seeds.

It is farther known by experience, that certain substances willhave a very different effect in promoting the luxuriancy of plantswhen added to pure sand and clay, from the effect they will havewhen added to sand and clay with which other substances havebeen previously mixed. Or, in other words, one manure will as-sist another in producing luxuriancy in the growth of the whole,or any part of a plant.

If one species of manure produces no effect when applied to amixture of sand and clay, unless another manure has been previ-ously, or afterwards, employed; and if the manure which it is ne-cessary to employ previously or afterwards, produces an effect,whether the other had been employed or not, which effect is, how-ever, greatly increased by the addition of that other manure, theeffect of the one manure must be that of producing an alterationin the other manure, or some alteration in the plant, by which itmay profit. *

All the experiments which have hitherto been made on the ad-dition of manures to sand or clay, have been performed only insmall pots, in such quantities as not to he at all applicable at large;or in some other manner, so that no certain conclusion can bedrawn from them. All other experiments on manures, particu-larly those made by practical formers, have always been uponsand and clay mixed with an unknown variety of other substances;-and carried on without any attempt to investigate what these other-matters were.

It is therefore proposed, that some effectual experiments shouldbe made upon sand and clay, mixed together in such proportionsas may be rendered rich soil. For this purpose, a field should bechosen, naturally consisting of such a mixture; known by expe-riment to be from one fifth of clay and four-fifths of sand, to half

* A manure may be itself the food of plants, or it may be of a kind that'viU bring other manures to a state adapted to their digestive powers, or it mayexcite in the plants themselves an operation which may cause other manures tobe digested, that otherwise would not have been so, or may render an imperfect;digestion complete. A buttock of beef, for example, yields essential food forman; but if a man bad neither knives and forks, nor teeth, nor any other modeof cutting it in pieces, it could not be swallowed, and, even if swallowed, itcould not be digested in a weak stomach, unless pepper, or some other stimu-lant, were thrown in with It. Neither the knives and forks, the teeth, nor thepepper, give nourishment to a man ; yet, without them, the beef, which givestlie nourishment, could not be digested. Now, the question, with regard to ma-nures, when different sorts are mixed together, is, which of them represent diebuttock of beef, which of them the knives and forks, and teeth, and which ofthem the pepper ? One principal object of the proposed experiments is to.de-cide this point, which authors arc by no means agreed about, although it lie thefoundation of agriculture.