PRACTICAL CUI/rUIiE OF PLANT.?. 



671 



been previously stated, tliat the elementary con- 

 stituents of all vegetable bodies consist of oxy- 

 gen, hydrogen, and nitrogen gases, with carbon, 

 and a few of the earthy salts, and it must be 

 evident that substances furnishing these ele- 

 mentary matters, and in a condition best suited 

 for absorption by the organs of plants, are those 

 best adapted as manures. 



Animal and vegetable substances in a state of 

 decomposition, and some earthy and saline mat- 

 ters, constitute the ditferent kinds of manure. 

 •According to the experiments of Sir H. Davy,* 

 all substances entering into the composition of 

 vegetable manure or food, must be in a state of 

 fluiditj', or in the form of gas or air. The 

 great object, therefore, in the application of 

 manure, should be to make it afford as much solu- 

 ble matter as possible to the roots of the plant, 

 and that in a slow and gradual manner, so that 

 it may be entirely consumed in forming its soft 

 and organized parts. 



IMucilaginous, gelatinous, saccharine, oily and 

 extractive fluids, carbonic acid, and water, ai-e 

 substances that, in their unchanged state, con- 

 tain almost all the principles necessary for the 

 life of plants ; but there are few cases in which 

 they can be applied as manure in the pure form, 

 and vegetable manures in general contain a great 

 excess of fibrous and insoluble matter, which 

 must undergo chemical change before it can be- 

 come the food of plants. The nature of the che- 

 mical changes in these substances may thus be 

 briefly stated. If any fresh vegetable matter 

 which contains sugar, mucilage, starch, or other 

 of the vegetable compounds soluble in water, 

 be moistened and exposed to air, at a tempera- 

 ture from 55° to 80°, oxygen will soon be ab- 

 sorbed, and carbonic acid formed, heat will be 

 produced, and elastic fluids, principally carbonic 

 acid, gaseous oxide of carbon, and hydro-car- 

 bonate, will be evolved ; a dark-coloured liquid, 

 of a slightly sour or bitter taste, will likewise be 

 formed ; and if the process be suffered to con- 

 tinue for a time sufiiciently long, nothing solid 

 will remain, except earthy and saline matter, 

 coloured black by charcoal. The dark coloured 

 fluid formed in the fermentation always contains 

 acetic acid, and when albumen or gluten exists 

 in the vegetable substance, it likewise contains 

 volatile alkali. In proportion as there is more 

 gluten, albumen, or matters soluljle in water in 

 the vegetable substances exposed to fermenta- 

 tion, so in proportion, all other circumstances 

 being equal, will the process be more rapid. 

 Pure woody fibre alone undergoes a change very 

 slowly, but its texture is broken down, and it 

 is easily resolved into new aliments, when mixed 

 with substances more liable to change, contain- 

 ing more oxygen and hydrogen. Volatile and 



* Agricultural Chemistiy. 



fixed oils, resins, and wax, are more susceptible 

 of change than woody fibre, when exposed to 

 air and water, but much less liable than the 

 other vegetable compounds ; and even the most 

 inflammable substances, by the absorption of 

 oxygen, become gradually soluble in water. 

 Animal matters in general are more liable to 

 decompose than vegetable substances, oxygen is 

 absorbed, and carbonic acid and ammonia formed 

 in the process of their putrefaction. They pro- 

 duce foetid compound elastic fluids, and likewise 

 azote ; they afford daik coloured acid and oily 

 fluids, and leave a x'esiduum of salts and earths, 

 mixed with carbonaceous matter. 



The principal substances which constitute the 

 different parts of animals, or which are found 

 in their blood, their secretions, or their excre- 

 ments, are gelatine, fibrin, mucus, fatty, or oily 

 matter, albumen, urea, uric acid, and other 

 acid, saline, and earthy matters. 



Whenever manures consist principally of mat- 

 ter soluble in water, it is evident that their fer- 

 mentation or putrefaction should be prevented 

 as much as possible, and the only cases in which 

 these processes can be useful, are when the man- 

 ure consists principally of vegetable or animal 

 fibre. The circumstances necessary for the pu- 

 trefaction of animal substances, are similar to 

 those requii'cd for the fermentation of vegetable 

 matters — a temperature above the freezing point, 

 the presence of water, and of oxygen, at least in 

 the first stage of the process. To prevent man- 

 ures from decomposing, tliey should be pre- 

 served dry, defended from the contact of air, 

 and kept as cool as possible. Salt and alcohol 

 appear to owe their power of preserving animal 

 and vegetable substances to their attraction for 

 water, by which they prevent its decomposing 

 action, and likewise to their excluding air. 



We shall here enumerate a few of the different 

 kinds of manures. All green succulent plants 

 contain saccharine or mucilaginous matter, with 

 woody fibre, and readily ferment. Such should 

 therefore, if intended for manure, boused as soon 

 as possible after their death. Hence the advan- 

 tage of digging in green crops, whether natural 

 or sown on purpose; they must not, however, be 

 turned in too deep, otherwise fermentation will 

 be prevented by compression and exclusion of 

 air. Green crops should be dug in, if it be pos- 

 sible, when in flower, or at the time the flower 

 is beginning to appear ; for it is at this period 

 that they contain the largest quantity of easily 

 soluble matter, and that their leaves are most 

 active in forming nutritive matter. Green crops, 

 bind weeds, or the parings of hedges or ditches, 

 require no preparation to fit them for manure, 

 nor does any kind of fresh vegetable matter, 

 The decomposition slowly proceeds beneath the 

 soil, the soluble matters are gradually dissolved, 

 and the slight fennentation which goes on, 



