WITH REFERENCE TO HORTICULTURE. 23 



not readily decomposed by fermentation. The burning of vegetable 

 substances must necessarily dissipate the whole of the oxygen, 

 hydrogen, and nitrogen which they contain, together with more or 

 less of the carbon, according to the degree in which the burning mass 

 is exposed to the action of the atmosphere. Hence in burning wood 

 for charcoal, the pile of logs is covered with earth or mud to prevent 

 the production of flame, and consequent decomposition of the carbon, 

 by the action of the oxygen of the atmosphere. The burning of 

 vegetables, however, does not destroy the fixed saline ingredients 

 which they contain ; and hence vegetable ashes, as manure, will be 

 valuable as containing salts which are either of general or specific use 

 to plants, and also as containing more or less carbon. If one kind of 

 plant only were burnt at a time, then the ashes of that plant would 

 form a specific manure for plants of the same kind ; but as a number 

 of kinds are generally burned together, their ashes must contain salts 

 of various kinds, and they may be considered as being useful to plants 

 generally. Among these ashes there is always a large proportion of 

 vegetable alkali (carbonate of potass) ; and this, when mixed with soil, 

 combines with insoluble organic matter and renders it soluble; and hence 

 vegetable ashes form a useful manure for all soils, since potass is of 

 almost universal existence in plants. It is therefore not only a general 

 manure by its action on organic matter, but a specific constituent of 

 plants. Soda, which exists but in few plants, differs from potass in 

 not being a specific manure, its action being limited to increasing the 

 solubility of organic matter already in the soil ; and in performing 

 this office, it is found to be more efficient than potass. 



Soot is composed of the various volatile matters derived from the 

 burning of coal or wood, together with carbon, and earths which have 

 been mechanically carried up the chimney with water in the form of 

 smoke. From experiment it appears that soot owes its value as a 

 manure to the saline substances which it contains ; and these are 

 chiefly the carbonate and sulphate of ammonia, together with a small 

 quantity of bituminous matter. The fact of carbonate of soda 

 proving useful as a manure is undoubted, though it is difficult to 

 explain in what manner it acts, unless, like saltpetre, it stimulates the 

 roots. Soot when applied in gardens is generally strewed on the sur- 

 face, and it is considered offensive to snails, slugs, and worms; though 

 by no means killing them, as is frequently supposed. Its effects are 

 rarely perceptible after the crop to which it is applied : and therefore, 

 like liquid manures, soot affords a quick return for the capital em- 

 ployed in it. 



Street manure, or that which is swept up in the streets of towns, 

 consists of a great variety of matters, animal, vegetable, and mineral. 

 In the manner towns are now kept, it is smaller in quantity and of less 

 value than formerly, when it was among the richest of all manures. When 

 collected in quantities, even though containing a large proportion of 

 earth and coal ashes, it ferments powerfully, and will continue giving 

 out heat throughout a whole summer. For this purpose it has been 

 u>t-d in forcing-gardens as a substitute for tanners' bark and stable- 



