200 CAUSE OF MANURING VALUE OP CLOVER. 



from equal spaces, and after being perfectly cleared of the adhe- 

 ring earth, were dried, weighed, and also portions of each analyzed. 

 Of the two crops of wheat of that year, averaged, he found the 

 whole residue of stubble and roots to be per acre : 



(from grain, weighing, Ibs. 1075) Ibs. 644 

 Residue of clover 



stubble and roots (from hay, Ibs. 2292) 1833 



Eesidue of oat stubble and roots (from grain, Ibs. 1862) " 836 



The residues of wheat and oats each contained per acre 2 Ibs. of 

 azote only; while the residue of the clover contained 26 Ibs. Of 

 course the superiority of the latter in quantity, great as it was over 

 the other residues, was still greater in richness, or quality for 

 manuring. 



While all persons have concurred in asserting the meliorating 

 effects of clover and other leguminous crops, there has been as 

 general an erroneous agreement as to the cause of this quality. It 

 has been assumed by our scientific instructors, and their doctrine 

 was received without question, that plants with broad leaves ab- 

 sorbed more carbon from the air, and hence the superiority in this 

 respect of leguminous plants over all of the narrow-leaved tribes. 

 Never was there an opinion more generally admitted on a weaker 

 foundation, or more easy to overthrow. Several cultivated crops, 

 as tobacco, palma-christi. cabbage, turnip, pumpkin, and other like 

 vines, have much broader leaves than any of the legumes ; but 

 neither of these has ever been deemed to have any peculiar power 

 for manuring by its growth and decay on the land. Nearly all 

 forest trees also have very broad leaves, and they exhibit no su- 

 periority of manuring qualities on that account, whether compared 

 with narrow-leaved trees, or with leguminous crops. But is enough 

 to refer to the numerous analyses of plants reported by chemists, 

 all of which, like those in the table copied on a preceding page 

 (244) go to show that clover, beans, peas, vetches, &c., have in 

 general no larger proportions of carbon than other and even the 

 most exhausting plants. Indeed, of this element there is a close ap- 

 proximation to equal proportions in all plants whose constituent 

 parts have been reported. The proportion usually varies between 

 45 and 50 per cent, of the whole dry weight of the plant. From all 

 these facts, it may be inferred as being nearly a correct rule, that in 

 general the plants or crops which yield the greatest quantity of total 

 product to the acre, in dry weight, will have taken up (from all 

 sources, and of course mostly from the atmosphere) the largest 

 amount of carbon; and therefore will return more to the land if 

 left to act as manure. "We must then look to other powers than 

 that of absorbing carbon for the cause of the superiority of clover 

 as manure which, as Boussingault says, is out of all proportion 



