on Permanent Meadoio Land. 
241 
addition of the nitrogen is not represented simply by tlie differ- 
ence between the prominently Lefiuminous produce by mineral 
manures alone, and the almost exclusively Graminaceous produce, 
when nitrogenous as well as mineral manures are employed. It 
will be obviously much nearer the truth to assume, that the arti- 
ficially supplied nitrogen — whether employed alone or in con- 
junction with mineral manures — ^was engaged in tlie production 
of at least the whole amount of increase above the produce witli- 
cut manure. 
In fact, it is not impossible that, in even this mode of estimate, 
the degree in which the artificially-supplied nitrogen has been 
involved in the amount and composition of the produce, is some- 
what understated. For, even the unmanured produce contained 
more of the highly-nitrogenized Leguminous herbage, than did that 
grown by either ammoniacal salts alone, or by ammoniacal salts 
in conjunction with mineral manure. Hence, it might be con- 
cluded, that the point beyond which the artificially-supplied 
nitrogen became involved in the production of Graminaceous in- 
crease, would be even lelow that represented by the acreage yield 
of nitrogen without manure. For, that amount depended ma- 
terially upon the quantity of the highly Leguminous herbage in 
the unmanured produce, which was at once diminished on the 
addition of nhrogenous manures. 
For the above reasons, then, it is assumed that, at least the 
whole of the nitrogen in the produce by nitrogenous manures 
beyond that yielded on tlie unmanured plot may be calculated as 
due, in a certain sense, to that which was artificially supplied — 
whether or not the nitrogen was so supplied alone, or was aided 
in its action by conjunction with mineral manures. At the same 
time, it is freely granted, that the legitimacy of any estimates 
regarding the proportion of the nitrogen supplied by manure 
which is involved in the increase obtained by its use, must rest 
entirely on that of the assumption made as to the amount of the 
whole nitrogen of the produce, which is to be attributed to 
natural sources. It is not, indeed, possible, to obtain actual proof, 
that produce grown by nitrogenous manures has really assimi- 
lated neither more nor less of nitrogen from other sources, than 
that grown without them. It might be supposed that, with a 
ready supply of available nitrogen within a limited range of the 
soil, the plants would draw less upon the natural or unaided re- 
sources. On the other hand, it might be assumed that, with the 
increased vigour of growth due to nitrogenous manure, the feeders 
of the plant would be so extended, both above and under ground, 
as to increase its command over the natural resources of available 
nitrogen. It is obvious, therefore, that the best estimate to 
which our judgment can lead, cannot, after all, be looked upon 
VOL. XX. K 
