Agricultural Chemistry. 
493 
provided in the soil, and as to the greater reliance of the 
leguminous crops grown in alternation with them, upon atmos- 
pheric sources of nitrogen ; — and also his conclusion that the 
amount of produce in the rotation is in proportion to the 
nitrogen in the manure. 
Now, if M. Boussingault really did intend to say, " that legumi- 
nous plants alone possess the power of appropriating, as food, 
nitrogen from the air, and that other cultivated plants do not at all 
possess this property," he certainly here committed an error ; 
that is to say, if his meaning were, that the latter would assimi- 
late only the amount of nitrogen conveyed to the soil in the form 
of manure, and that they would not give a certain annual average 
produce independently of such supply. Such an error, if it 
were committed, would easily arise from the fact, that in his own 
experiments on the growth of wheat by means of manure, in 
which he only recovered in the produce about as much nitrogen as 
the manure contained, he had not by the side of his manured plot 
one growing the same crop without manure. By such a col- 
lateral experiment, he would have learned how much of his total 
produce was due to soil and season, independently of direct 
manure, and how much to the latter. Had he, indeed, possessed 
these data, he must then have concluded, that the cereals did 
accumulate a limited amount of nitrogen from natural sources ; 
and that the increase beyond this amount, was obtained only at a 
cost of much more nitrogen in the manure than was stored up 
in the increase of crop produced by it. And had M. Boussin- 
gault clearly appreciated this fact, regarding which, since the 
time he wrote, so much evidence has been recorded, he would 
scarcely, whilst so prominently calling attention to the distinctions 
which he observed in regard to the requirements of the cereals 
and leguminous plants in his rotations, nevertheless, have said, 
in reference to those admirable results, that they rather afforded 
a view of the circumstances of an entire rotation, than threw any 
light on the special share in rotation of the individual crops. 
Nor could he have failed to see, that in those distinctions which 
he really did point out, was the very key to the chemical prin- 
niples involved in rotation of crops. M. Boussingault, indeed, 
distinctly called attention to the fact, that the benefits derived 
from growing a leguminous crop before a cereal, must to a great 
extent arise from the amount of organic matter thus accumulated 
within the soil as a manure for the latter. He further pointed 
out, that the very restorative leguminous crops, nevertheless 
take from the soil a verv large proportion of some of the most 
important of the mineral constituents ; and from the latter fact 
he seems to have drawn the inference that in the choice of our 
succession of crops, cai'e should be taken to make the selection 
VOL. XVI. 2 K 
