94 
KOTAL HORTICULTURAL SOCIETY. 
accumulation, of assimilable nitrogen within the range of collec- 
tion of the crops which succeed it. On this view, not only does 
the growth of the Leguminous crop serve to arrest the loss of ni- 
trogen by drainage as nitric acid, by bringing up again much of 
that which had passed in that condition into the lower layers of 
of the soil ; but there is obviously provided one important ele- 
ment at least in the explanation of the beneficial effects of 
alternating Leguminous with Graminaceous crops in rotation. 
Again, the nitric acid would, most probably in great part, be in 
combination with lime, which is the base occurring in large pro- 
portion in the ash of our Leguminous crops ; and supposing ni- 
trogen were taken up by the plants as nitric acid, chiefly in 
combination with lime, but partly with potass or other bases, we 
should, in that fact, have an element in the explanation of the 
occurrence in the ashes of the Leguminosaa of so much fixed 
base, and especially of lime, not in combination with a fixed 
acid ; and we should, so far, to a less extent require the aid of the 
assumption that the bases in question had been taken up from 
the soil as ready-formed organic acid salts. 
The above considerations are of interest not only with refer- 
ence to the results obtained in the highly manured garden- soil, y 
but also in connexion with the facts of the entire failure in the 
field at the present time where neither carbonaceous nor nitro- 
genous manures have been supplied, and lime has been the most 
exhausted, and of the partial success where carbonaceous and 
nitrogenous manures have been to a considerable extent supplied, 
and lime has been added in great excess. 
It is obvious that the time that would serve for the formation 
and distribution of the organic acid salts, or of the nitrates, 
would also serve for the soil-digestion, and distribution, of mineral 
constituents. 
To conclude, in regard to the conditions of failure and partial 
success in the field at the present time, it may be remarked that 
on some portions of the land where there is the complete failure, 
considerably more of those mineral constituents which most cha- 
racteristically increase the growth of a healthy clover crop in the 
land in question, have been supplied than taken off in the crops. 
This has not, however, been the case with the nitrogen on any 
portion of the experimental land ; though, as already said, the 
exhaustion of it has nowhere been so great as in experiments 
on mixed herbage, including perennial Leguminous species. On 
