COMPOSITION OF PLANTS. 225 



poWGifuI, produces little effect upon the second crop. When 

 the manure, liowever, has passed through this fermentation, 

 it will for ever connnunicate extractive matter and carbon to 

 the soil ; but before these can serve for the nourishment of 

 })lants, they must again be combined with the oxygen of the 

 atmosphere. 



The burning of the soil, too, operates by the production of 

 oxygenised carbon, because every burning ends with the attrac- 

 tion of oxygen. Hence also arises the advantage of smoking 

 the ground, as it is practised in Italy ; (Bertuch Garten Ma- 

 gazin, b. 3. sec. ilSd.) Ashes must be considered as carbon 

 half oxidated durinjj the burnins:, and united with alkali. 

 Accordingly, when they are laid out, they have a powerful 

 influence in the melioration of the }X)orest soils, as is proved 

 by the excellent example of the improved agriculture around 

 Dankerode, south from Harzgerode ; (Georg. in den Mogelin- 

 schen Annalen, b. 3. s. 419, 448.) 



The green manuring (sovescio of the Italians) proves tlie 

 same fact ; but the slow fermentation of green vegetables 

 should only be employed in fertile and warm soils. Potato 

 plants, Zostera marina, and the common sea-ware, serve as 

 manure, in the same manner, by the fermentation which they 

 undergo in the soil. 



Lastly, Nothing proves the truth of this account more 

 clearly, than the distinguished advantage which the soil de- 

 rives from calcareous matter ; since the attraction of this sub- 

 stance for carbonic acid is, as every person knows, very pow- 

 erful. The most luxuriant vegetation arises on calcareoua 

 soils ; the strongest wood in the wc^-ld grows in the calcareous 

 islands, which are formed by the Coral Reefs of the South 

 Sea, as also upon the volcanic tei'ritory of IVIascaren's Island. 

 By a mixture of lime, we prepare tlK? best compost, when it 

 is placed in layers between animal manure, clay, and old 

 mud. The powerful effect of Chara vulgaris in fertilising 

 land, depends on the calcareous shme with which it is covered, 



348. 

 Not only carbonic acid water, but also the azote which is mix- 

 ed with it, constitutes a principal part of the peculiar nourish- 



