102 Report of Experiments on the Growth of Wheat. 
In the earlier years of the experiments the manures were each 
season allotted with a view to the settlement of certain individual 
points ; such, for instance, as the effect of individual mineral 
manures, the necessity or otherwise of providing carbonaceous 
organic matter, and the effect, on the one hand of a deficient or 
partial, or on the other, of a full or excessive, manuring in one 
season on the crop of the immediately succeeding season. The 
allotment was always made with more or less of special reference 
to the previous manuring and produce of the respective plots ; 
but, unfortunately, not with that full appreciation of the desirable- 
ness of maintaining exactly and easily comparable relations 
between one plot and another for a long series of consecutive 
seasons, which, in this hitherto untrodden path of inquiry, could 
only be attained by a careful study of the results from time to 
time obtained. 
The manures applied on one and the same plot were, indeed, 
much more uniform from year to year after the first three, or 
even in many cases after the first two years of the experiments. 
There were, however, still some variations in the description, 
and more in the amount employed on the same plot, even up to 
the eighth year inclusive ; though, during the last four of these, 
there were comparatively few the effect of which would be to 
interfere materially with the comparative character of the results 
obtained in subsequent seasons. 
In the ninth year it was definitively arranged to supply, 
throughout the field, the same manure year after year, on the 
same plot, for many successive seasons, so as to trace more 
clearly the point at which one or another constituent became ex- 
hausted, or in excess, in relation to others, or to the requirements 
for the production of a maximum crop. 
It is obvious, therefore, that when comparing the results 
obtained on one plot with those of another in the ninth and eleven 
succeeding seasons, the previous history of each plot must be 
taken into consideration. Numerous illustrations will, indeed, be 
given of the effects of the unexhausted residue of nitrogenous and 
mineral manures applied in preceding seasons, on the amounts of 
produce obtained in succeeding ones ; not only, however, with 
a view to the more correct interpretation of the results obtained 
in the later years of these experiments, but also on account of the 
great practical importance of the question. But it will be when 
we come, on a future occasion, to discuss the deficiency or excess 
of certain constituents by the aid of analysis, that we shall enter 
more fully into the chemical statistics of each individual plot 
than is necessary, or even desirable, in presenting the outline of 
the results in their more practical bearings which it is proposed 
to give in the present paper. 
