464) Remarl{S and Observations suggested 



fits or losses derived from these soils depend on the heat and 

 moisture of the season : in a wet cold summer, the sandy soils 

 do best; in a warm dry summer, the clayey soils. Clayey soils 

 may be greatly benefited by draining, digging deep, pulverising, 

 and mixing with decomposing substances. Sandy light soils, 

 in some dry seasons, require treading and rolling to retain the 

 moisture. The most permanent and beneficial alteration, where 

 possible, is the mixing of the two together. In composts for pots, 

 plants will thrive in very different mixtures, according to the 

 heat and ventiliition they are exposed to, and the water they get. 

 Plants in light composts require more water and attention, and 

 will grow more quickly; while those in loamy composts, if well 

 drained, are hardier and firmer, and do not need so much atten- 

 tion ; a medium is safest for plants, the cultivation of which 

 is not well understood. Oxide of iron is the most hurtful 

 principle to vegetation in soils, and may be easily detected from 

 its reel colour ; the best corrective for this is lime, which neu- 

 tralises the acid. 



Much has been said about manures by chemists ; but the 

 benefits hitherto derived from the details of chemical analysis in 

 practice has not been correspondingly great. The conclusion 

 arrived at by Sir Humphry Davy was, that all manures should 

 be put into the ground in as recent a state as possible, while, in 

 practice, the opposite plan is thought more beneficial. Most 

 pi'actical men are of opinion that the ammonia fii'st given off' by 

 manures is very prejudicial to plants; and manure, when kept in 

 a heap, does not lose much besides this, and is more perfectly 

 rotted in a heap than when spread in the soil. A mixture of 

 horse and cow dung, rotted to the consistence of a black oily 

 peat, is thought the most economical and advantageous way of 

 applying manure. Chemical analysis shows that all the parts of 

 plants are chiefly composed of carbon, hydrogen, and oxygen ; 

 nitrogen has lately been more often detected than formerly ; 

 and small quantities of other substances, as silex, and other 

 stones, metals. Sec, are sometimes found ; but the first three are 

 the component parts of all plants, and the food of plants should 

 therefore consist of substances furnishing these in greatest plenty. 

 Hydrogen and oxygen are furnished by the decomposition of 

 water ; oxygen and nitrogen from the air. Carbon is produced 

 from animal and vegetable substances, being only in small quan- 

 tity in the air ; but, before it can enter the spongioles of the 

 roots, it must be converted into carbonic acid, which is produced 

 by fermentation causing the oxygen of the air to unite to the 

 carbon, and form carbonic acid : hence the necessity of a proper 

 degree of fermentation in manure, and the great benefit of 

 applying yeast, and other fermenting substances, to manures. 

 In the act of fermentation, too much heat is sometimes evolved, 



