CALCAREOUS MANURES-THEORY. 4-7 



cultivated, nor again observed, until tlie second summer afterwards. At 

 that time, the piece remained as bare as formerly, except along the filled 

 gullies, which, throughout the whole of their crooked courses, were covered 

 by a thick and uncommonly tall growth of sorrel, remarkably luxuriant for 

 any situation, and which, being bounded exactly by the width of the nar- 

 row gullies, had the appearance of some vegetable sown thickly in drills, 

 and kept clean by tillage. So great an effect of this kind has not been 

 produced within my knowledge — though facts of like nature, and leading 

 to the same conclusion, are of frequent occurrence. If small pines stand- 

 ing thinly over a broom-grass old-field are cut down and left to lie, under 

 every top will be found a patch of sorrel, before the leaves have all rotted. 

 3rd. The growth of sorrel is not only peculiarly favored by the application 

 of vegetables containing acids already formed, but also by such matters 

 as will form acid in the course of their decomposition. Farm-yard manure, 

 and all other putrescent animal and vegetable substances, form acetic acid 

 as their decomposition proceeds.* If heaps of rotting manure are left 

 without being spread, in a field but very slightly subject to produce sorrel, 

 a few weeks of growing weather will bring out that plant close around 

 every heap ; and for some time the sorrel will continue to show more bene- 

 fit from that rank manuring than any other grass. For several years my win- 

 ter-made manure was spread and ploughed in on land not cultivated until the 

 next autumn, or the spring after. This practice was founded on the mis- 

 taken opinion, that it would prevent much of the usual exposure to evapo- 

 ration and waste of the manure. One of the reasons which alone would 

 have compelled me to abandon this absurd practice was, that a crop of 

 sorrel always followed, (even on good soils that before barely permitted a 

 scanty growth of it to live,) which so injured the next grain crop as greatly 

 to lessen the benefit from the manure. Sorrel unnaturally produced by 

 such applications does not infest the land longer than until we may suppose 

 the acid to have been removed by cultivation and other causes. 



It may be objected, that even if fully admitted, my authorities prove only 

 the formation of a single vegetable acid in soil, the acetic— that my facts 

 show only the production of a single acid plant, sorrel— and that the acid 

 which sorrel contains is not the acetic, but the oxalic.f In reply to such 

 objections, it may be said, that from the application of acids to recently 

 ploughed land, no acid plant except sorrel is made to grow, because that 

 one only can spring up speedily enough to arrest the fleeting nutriment. 

 Poverty grass (Aristida, gracilis or A. dichcAoma) grows only on the same 

 kinds of soil, and generally covers them after they have been a year free 

 from a crop, but does not show sooner; and pines require two years before 

 their seeds will produce plants. But when pines begin to spread over the 

 land, they soon put an end to the growth of all other plants, and are abun- 

 dantly supplied with their acid food, from the dropping of their own leaves. 

 Thus they may be first supplied with the vegetable acid ready formed in 

 the leaves, and afterwards with the acetic acid formed by their subsequent 

 slow decomposition. It does not weaken my argument that the product 

 of a plant is a vegetable acid different from the one supposed to have nou- 

 rished its growth. All vegetable acids (except the prussic) however diffe- 

 rent in their properties, are composed of the same three elementary bodies, 

 differing only in their proportion sf- and consequently are all convertible 

 into each other. A little more, or a little less of one or the other of these 



* Agr. Chem. p. 187. (Phil, ed.) 



t Agr. Chem. Lecture 3. 



X Carbon, oxygen, and hydrogen. Agr. Chem Lecture .3, p. 78. 



