526 GARDEN MA^'AGEMl:^T. 



is gaseous, and for this reason cannot be employed directly by the cultivator, 

 who, were he to try to create an atmosphere of the carbonate of ammonia 

 imder his ground, would spend a great deal of money without obtaining any 

 benefit whatever, since the shghtest movement of the air would instantly 

 produce evaporation of this volatile manure." 



1 64 1. It thus appears that ammonia, whether in the atmosphere or the 

 soil, is the great source of fertility ; but natural soils are themselves of much 

 importance in plant-cultivation. Eich black mould often contains 20 per 

 cent, of its own weight of the organic matter we have described. In peat- 

 earth, the proportions vary from 60 to 70 per cent. ; in good garden land, the 

 average amount is 10 to 12 per cent. ; and in average soils of the fields, it may 

 be 6 or 7 per cent. Sand in its various phases, from silver to yellow, is an im- 

 portant part of the compost-heap, more for its mechanical than its fertilizing 

 properties, although it fonns a constituent of many plants ; and clay, besides its 

 stiff, tenacious character, which enables it to sustain the more vigorous veget- 

 able gTOwi;hs, is found to be highly attractive of ammonia ; so highly attractive, 

 according to Mr. Way, that an ammoniacal sulphate, or nitrate, or muriate, 

 being filtered through a collection of clay soils, real chemical decomposition 

 resulted, the ammonia being retained, and the associated acid passing into some 

 new state of combination. Pursuing his experiments, Mr. Way finally de- 

 termined the question by tracing sihcates of lime, of soda, and potash among 

 the constituents of clay, which were the absorbing agents in question. It is 

 thus a question of great practical importance that the soils for gardening 

 pm-poses should not only be judiciously, but carefully harvested. All the care 

 bestowed on a plant in potting and watering is so much labour thrown away 

 if the soil is unsuitable ; but if a suitable soil be employed, it is wonderful 

 with what tenacity a plant will cling to existence, even under the most un- 

 favourable circumstances. The sweeter a soil is, that is to say, the more it 

 has been exposed to atmospheric influences, the more suitable it becomes for 

 all horticultural purposes. 



1643. Even maiden soil from an upland pasture, where it has been well 

 drained, is materially improved by exposure to atmospheric changes for a few 

 months ; while soil from a wet locality should never be used, under any cir- 

 cumstances, until it has been exposed to the varied changes of an English 

 winter ; and if it be also exposed for a month or two in summer, it will be 

 much improved. The improvement ai'ises principally from the expulsion of 

 deleterious matter, the decomposition of vegetable substances, and the tho- 

 rough disintegration of the whole mass. When a soil is very strong and 

 adhesive, it is necessary to expose it in thin layers to the action of frost, 

 removing the frozen part as often as it becomes frozen to a sufficient thick- 

 ness, and placing it where it can be thoroughly dried. Soil thus prepared 

 will generally be found clear of insects, a matter of considerable importance 

 in the cultivation of choice plants. 



1643. P®^* should be in layers not more than two inches thick, firm in 



