109 
carbon was raised to 8.383 kilogrammes; thus 5.400 of 
carbon was furnished by the carbonic acid of the air. In the 
same rotation, the azote primarily included in the dung 
weighed 157 kilogrammes. By culture, the weight attained 
251, and the atmosphere had furnished 94 kilogrammes of 
azote. 
In another rotation, the carbon of the crops surpassed the 
carbon of the dung by 7.600 kilogrammes, and the azote was 
increased to 163 kilogrammes. 
If, therefore, the plants receive three times as much carbon 
from the air as they do from the soil, as is proved by these 
experiments, supposing them to have assimilated the whole 
carbon of the manure without any being lost, which is very 
improbable, and if the carbon derived from the soil must be 
combined with oxygen as carbonic acid, I think we may from 
these facts deduce several important results. 
1. That manures are useful only during the process of 
their decay, or as long as they alford carbonic acid, and 
therefore are to be applied during an early period of their 
fermentation; and hence also that soils, and the manures 
contained in them, require to be aerated as well as watered. 
2. That crops exhaust, not in proportion to the quantity 
of nutritive matter contained in the crops produced (for then 
we should tacitly acknowledge that all the organic matter of 
plants originates in the soil), but that those plants which 
receive the most elementary matter from the atmosphere, ex- 
haust the least ; and Liebig proves that plants receive from 
the atmosphere in proportion to the size of their leaves and 
green parts ; and, therefore, the leguminosoe, the clover, po- 
tatoes, and turnips, &c., exhaust less than the cerealia. 
3. That if plants receive so large a proportion of their 
carbon from the atmosphere, and in fact can receive the 
whole, as proved by the experiments in calcined sand, then 
it will follow that all manures which contain simply carbon, 
oxygen, and hydrogen, as simple straw, &c., whether fer- 
