1846.] Theory of Agriculture. 9 



the atmosphere surrounding the leaves, or from the soil, Bou- 

 singault seems to consider settled in favor of the latter souice, by 

 his own experiment detailed p. 41 of Rural Economy. Thus in 

 our experiment, wliere the air contained 0.0004 carbonic acid, 

 after it had passed in a current over the branch of a vine in a 

 glass balloon, it contained only 0.0001 carbonic acid, three- 

 fourths of the whole quantity having been absorbed by the leaves 

 of the vine. He says, nevertheless, that in operating with the 

 same apparatus in the night, opposite results were obtained. The 

 air in traversing the balloon generally acquired a quantity of car- 

 bonic acid, the double of that which the atmosphere contained at 

 the same moment. 



This being the fact, it appears to us to prove one thing, viz., 

 a constant supply of carbon under all circumstances, by night or 

 by day for the soil, though it may be that it is only assimilated 

 during sun light; but this is not proved, for there are some facts 

 which seem decidedly opposed to this view: some vegetables 

 grow far more vigorously in the night; the hop, and especially 

 the pumpkin vine: the latter has been known to grow five feet 

 in three nights. In this instance there must have been a fixation 

 of carbon in the absence of light. But this is not the place for 

 the discussion of this point. 



In the preceding pages we have seen that Liebig takes the 

 ground, that the atmosphere furnishes all the carbon of plants, 

 and his views are so expressed that most readers, if not all, un- 

 derstand him as saying, that the carbon is taken directly by the 

 leaves from the atmosphere, and that it is not introduced into the 

 tissues by the roots. It will be seen, too, that this doctrine rests 

 on what is put forth as a fact, that the quantity of soluble car- 

 bonous matter is totally insufficient to furnish the amount of car- 

 bon which is yearly taken up and fixed by any cultivated crop, 

 or even the amount which is fixed in a forest, consisting of pines, 

 firs, maples, beech and birch. 



It is time now to examine the truth of this doctrine. What 

 we propose to prove is, that, contrary to what Liebig says, there 

 is an abundance of soluble matter containing carbon in the soil, 



