4^ OF CARBON. 



that it becomes and remains perfectly insolu- 

 ble in water under any circumstances. 



These facts, which demonstrate plainly that 

 humus, or humic acid, cannot enter into the 

 composition of plants, have not been overlooked 

 by vegetable physiologists ; but they have sup- 

 posed, that, under certain circumstances, the 

 alkaline earths might act upon the humus, and 

 render it soluble, and thus in a fit state for the 

 assimilation of plants; but by calculations 

 made by the author of the work before quoted,* 

 it is proved beyond all question, that even sup- 

 posing humus in its most soluble compound, 

 that is as a humate of lime, to be absorbed by 

 plants, still that the produce of a given field so 

 far exceeds the quantity of humate of lime, 

 that could by any possibility either exist or be 

 created on such a field, under the most favour- 

 able circumstances, that some other cause must 

 be assigned for the source of nutrition to plants. 



Another argument that is conclusive on the 

 subject of humus not forming the nutrition of 

 plants is, that as humus is the result of the de- 

 cay of vegetable matter, from whence did the 

 first vegetables derive their supply of this sup- 

 posed necessary substance? 



We have seen in the analysis of hay that 

 100 parts consist of 44 parts carbon. Hence 

 the produce of an acre, weighing one ton must 

 contain about 985 pounds of carbon. An acre 

 of wheat also, yielding eight sacks, and weigh- 

 ing 2000lbs., must produce about 600lbs. of 



* Sprugel. 



