ON THE FOOD OF PLANTS, y 



which live in subterraneous places, this acid abounds ; but 

 by bringing them from almost perfect darkness gradually to 

 the light, this acid disappears, and the fibres proportionally 

 increase. This opinion is confirmed by some experiments 

 of Mr. Senebier, in which he observes, that " plants abun- 

 dantly supplied with water, which had been impregnated 

 with carbonic acid, transpired much more oxigen, than when 

 they were supplied with common water." % 



Some plants take more carbon than others into their com- Some plants 

 position; as for instance, the agaricus qnercinus, agaricus h ™* m ™* & 

 antiquus, boletus versicolor, boletus igniarius, boletus striaius, 

 boletus perennis, clavaria hypoxylon, clavaria pist Maris, and 

 many others. All these contain, from the result of analy- 

 sis, a quantity of carbon, nearly equal to all their other com- 

 ponent parts. But the lichen crispus, pinaster granulatut, 

 and lycopcrdon tessellatum, contain a very small portion of 

 carbon. 



Plants do not however retain all the carbonaceous mat- Th ^ Q not 

 ter they receive : they obtain more in the day when exposed retain all they 

 to light, than they naturally require; but by the absence of receive - 

 light they part with this surplus, and therefore yield respir- 

 able gas only in the day-time. 



The separation of oxigen from plants by radiant light Oxigen sepa- 

 seems to arise from the chemical affinity between oxigen and ™ ?°5 , 

 light. Fortius fact we are indebted to Dr. Ingenhousz ; and hidiogea* 

 but Humboldt was the first who ascertained, that hidrogen 

 gas applied to plants, even when excluded from the light, 

 occasions a separation of their accumulated oxigen. 



Some plants, as for instance, tremella nostoc, the Jilices, Oxigen retain- 



musci, and alsce, retain their oxigen weakly, and part with ed ™ th dlf?er * 

 ' . . , ent force, and 



it readily. And it is remarked by Van Uslar, to whom I affects the co- 

 am indebted for many of these observations, that such lour * 

 plants as contain much oxigen, and retain it obstinately, are 

 white; as for instance, our endive and celery, when excluded 

 from the light; while such as contain much oxigen, and 

 part with it easily, are generally green. 



If the analysis of plants leads us to consider carbon as one phnt« require 

 of the most essential articles in their composition and sup- ^getable 

 port, no less does the existence of ages prove to us, that the 

 principal source from which they derive their nutriment, 



whatever 



