Report of Experiments on the Growth of Wheat. 99 
other available form) was employed in subsequent seasons ; and 
so marked have been its effects, that the interest of the investiga- 
tion may be said almost to begin and end with the consideration 
of the influence of that important constituent of manures on the 
amounts and character of the produce obtained, in immediate 
or succeeding crops, according to the quantity employed, to the 
condition of the land in regard to the supply of available mineral 
constituents, and to the characters of the seasons. 
The Field Experiments. 
The particulars of the manuring and produce of each of the 
experimental plots, in each of the twenty years over which the 
experiments have extended, are given in detail in Tables I. to 
XXI. inclusive, in the Appendix ; and in Tables XXII. to 
XXVI. inclusive, also in the Appendix, are given some of the 
most important results in a more collective form. Those volumi- 
nous records, as above classified, show, respectively, the effects of 
one manure compared with another in each season separately, 
and the great difference of effect of the same manure in one 
season compared with another, and its increasing or diminishing 
effect when used year after year on the same plot. 
It will be obvious, however, on a very little reflection, that the 
question of the relative condition of exhaustion of the different 
plots cannot be satisfactorily considered by reference to the 
amounts of crop alone. To deal adequately with this part of the 
subject, the consideration of the chemical composition, as well as 
the amount, of the produce is obviously essential. Accordingly, 
the proportions of dry substance, and of mineral matter, in both 
the corn and the straw, of each plot, in each of the twenty years, 
have been estimated. The proportion, and amount per acre, of 
the nitrogen, and the composition of the ash, in both corn and 
straw, have in many selected cases been determined. The per- 
centage of nitrogen in the soil of some of the plots, at different 
stages of the progress of the experiments, has also been esti- 
mated. The mere tabular record of these results of analysis 
would occupy nearly as much space as those relating to the 
experiments in the field ; whilst the discussion of them, in their 
manifold and important bearings, would supply matter more 
than sufficient for a single paper. It is proposed, therefore, on 
the present occasion, to leave out of view the analytical results 
altogether, and to confine attention, almost exclusively, to the 
more salient points of interest brought out by the results of the 
field experiments alone, leaving the detailed treatment of the 
question of exhaustion to a future opportunity. 
The question of the climatic characters of the different seasons, 
and of the connexion between these and the amount and character 
of the produce yielded, would also require, for its due illustration 
H 2 
