62 ON THE FOOD OF PLANTS. 



the sense with which they are endowed is cne of the most essential, 

 while it is'not very probable that a whole class (Arachnids:} otherwise 

 very well organised, would be deprived thereof. 



[I may mention, that from experiments which I made near Havre 

 de Grace, in the summer of 1829, before the publication of M. Straus- 

 Diirckheim's work, I came to the same conclusion, and followed very 

 nearly the same train of reasoning with him, but with more numerous 

 illustrations, as may be seen in Insect Miscellanies, pp. 105 117, 

 all of which was written and printed, though not, I believe, published, 

 before his work. EDITOR.] 



ON THE FOOD OF PLANTS, PARTICULARLY HUMINE, 

 DERIVED FROM MANURES. 



BY PROFESSOR DE CANDOLLE OF GENEVA.* 



IN order to ascertain the general action of the multitude of manures 

 employed, it will be proper to analyse and compare them according to 

 the different ingredients of which they are composed. Carbon holds 

 the first rank ; though it is not only the absolute quantity, but the 

 state in which it is found, that determines its fitness to become the 

 food of plants. The substance most rich in carbon, such, for example, 

 as wood charcoal, is scarcely reckoned among manures, because in 

 this the carbon can only contribute very slowly to the formation of 

 carbonic acid, or humine (ulmine), by its combination with the air, and 

 cannot, therefore, form soluble materials to be taken up by the roots. 

 It is only after a very long interval that it undergoes these changes, 

 and then it acts really as a manure, as is proved by the fresher green 

 of the plants on old charcoal stations in the forests. 



The refuse (marc) of sugar refineries, which contains a great quan- 

 tity of animal charcoal, mixed, or combined with portions of burnt 

 sugar, forms a manure much valued in the vicinity of these factories.f 



All the substances, which contain different proportions of carbon, 

 furnish food for plants; first, because the oxygen of the air unites 

 by simple affinity with a portion of this carbon to form carbonic acid, 

 or because a certain quantity is disengaged by fermentation ; in both 

 of which cases, the carbonic acid is dissolved in the water of the soil, 

 and being taken up by the plant, it serves as food. Secondly, these 

 matters are more or less disposed to dissolve in the water itself of 



* Translated by the Editor from the French work (t Physiologic Vegetable," a work 

 which every philosophical Botanist ought to possess, 

 f Payen, Annales Soc. d' Hort. de Paris, 1827, p. 171. 



