t> ORGANIC MANURES, CONSIDERED 



177. Soils are improved by the modes in which they are cultivated ; as for 

 example, by the order in which crops are made to succeed each other, by 

 fallowing, by resting, and by the manner in which water is applied to grow- 

 ing crops ; but these subjects will come under notice when we are treating 

 of the practice of Horticulture. 



CHAPTER III. 

 MANURES CONSIDERED WITH REFERENCE TO HORTICULTURE. 



178. THE improvement of the composition and the texture of a soil, and 

 of its condition with reference to water and heat, will have but little effect 

 on the plants cultivated in it, without the addition of manure ; for this 

 article, it must be borne in mind, is the food of plants, while the soil is only 

 the stomach, or laboratory, in which that food is digested and rendered fit 

 for being taken up by the spongioles of the roots. In order to determine 

 what substances are suitable for becoming manures, it is useful to know what 

 are the constituent elements of plants. Of these we shall find that some 

 elements are common to all plants whatever, such as carbon with oxygen 

 and hydrogen in the proper relative proportions for forming water, and 

 nitrogen ; while some elements are only found in particular plants, such as 

 certain salts, earths, and metallic oxides. Every plant, therefore, may be 

 said to have its general or common food, and its specific or particular food ; 

 and hence, in this point of view, manures may be classed as common and 

 specific. The most perfect manure for any plant would therefore seem to 

 be, that plant itself in a state of decomposition ; but as the purpose for which 

 plants are cultivated is to supply food, clothing, and various constructions 

 and contrivances, for animals, hence, in a state of civilisation, it is among 

 these, and from animals themselves, that we must seek for the most suitable 

 manure for plants. The various substances which have been used for manures 

 may be classed, with reference to their effect on plants, as general and speci- 

 fic ; and with reference to the soil, as improving, enriching, and stimulating. 

 Improving manures are such as, while they afford positive nourishment or 

 stimulus, add some permanent matter to the soil ; such as lime, chalk, marl, 

 bones, &c. Enriching manures are such as supply only nourishment to 

 plants ; such as stable manure, and every description of organic matter ; and 

 stimulating manures are such as serve to aid in the decomposition of, or 

 otherwise operate on, the organic matter. As some manures, however, par- 

 take in an equal degree of more than one of these properties, such as lime, 

 which is both a stimulating and improving manure, the most convenient 

 arrangement of manures will be organic, inorganic, and mixed. 



SECT. I. Organic Manures. 



179. Organic manures must obviously be either of animal or vegetable 

 origin. Purely vegetable manure is exemplified in leaf-mould, malt-dust, rape- 

 cake, spent tanner's bark, some kinds of peat, and green vegetables when 

 they are buried in the soil in a living state. 



180. Leaf-mould is perhaps the most universal manure for garden plants, 

 because, when thoroughly decomposed, the most tender kinds will live in it, 



