218 Experiments on the Growth of Wheat. 
this last 20 bushels of the total 53 of increase were derived from 
the mineral manures employed. This is, therefore, conclusive 
proof that these minerals were supplied to the land in a form 
capable of being rendered available for the growth of the plants ; 
and it is therefore clear that the inability of the minerals when 
used alone, to increase the assimilation of organic constituents 
from natural sources, was not due either to their not containing 
soluble silica or other mineral matters required bj the wheat- 
plant, or to an unavailable form of those constituents which were 
supplied. 
In the next Experiment (No. 6), the manure consisted of 
2000 lbs. of rape-cake per acre. As already explained, rape-cake 
contains a large amount of carbonaceous organic matter, a consi- 
derable quantity of nitrogen, and also some mineral matter. The 
quantity applied — namely, 2000 lbs. — was estimated to supply 
annually about the same amount of nitrogen (but in a different 
form of combination) as the ammoniacal salts in Experiments 3, 
4, and 5 respectively. It also supplied as much of the more im- 
portant minerals as would be contained in the increase of produce 
which was obtained by it. If, therefore, the total increase of 
produce obtained by the rape-cake should be pretty nearly the 
same as that yielded by the minerals and ammonia of No. 5, 
which contained, as has been said, nearly the same amount of 
nitrogen, but no carbonaceous organic matter, we can only conclude 
that the latter in the rape-cake has had little to do with the 
increase ; and, in fact, that this is attributable to the supply of 
nitrogen and minerals afforded by the rape-cake. A comparison 
of the results obtained by the nitrogen and minerals of No. 5, 
and by the nitrogen, minerals, and carbonaceous organic matter of 
No. 6, shows that, taking the average of the 4 years, the latter 
gives about half a bushel per annum more corn, but about 90 lbs. 
less straw than the former. It is true that although the average 
produce of the minerals and ammonia of No. 5 and that of the 
rape-cake of No. 6 are so nearly identical, yet the produce of the 
two varies considerably in the individual years ; but this can 
scarcely be wondered at, when it is remembered in what a very 
different form the nitrogen existed in the two manures, and also 
how differently the degree of their solubility, and consequently 
the stage or tendency of growth of the plant, would be influenced 
by equal conditions of climate. The average results are, how- 
ever, as already stated, all but identical, and we are therefore 
justified in deciding that in this experiment, as well as in the 
former ones, the increase of produce was measured by the amount 
of nitrogen supplied by the manure in a form available for the 
growth of the crop — provided, of course, the necessary minerals 
were not absent; and further, that the carbonaceous organic 
