mi. J. II. GILBERT ON CLOVER-SICKNESS. 
91 
taken as absolute proof of failure of the manurial conditions 
supplied on the various small plots ; for not only was the 
summer of 1870 one of extraordinary drought, but where the 
manures were applied at the different depths specified, the land 
may not yet have recovered a favourable mechanical condition, 
and where the natural soil was replaced by that from the garden 
border, the plants, being luxuriant compared with any around 
them, were more a prey to woodpigeons, rabbits, and game. 
The whole of these small plots are now resown, and those of 
the garden-soil are entirely enclosed, both around and above, by 
galvanized wire netting. 
The general result of the experiments in the field is — that 
neither organic matter rich in carbon as well as other consti- 
tuents, nor ammonia-salts, nor nitrate of soda, nor mineral con- 
stituents, nor a complex mixture, supplied as manure, whether 
at the surface or at a considerable depth, has hitherto availed 
to restore the clover-yielding capabilities of the land. 
On the other hand, it is clear that the garden-soil supplied the 
conditions under which clover can be grown year after year on 
the same ground for many years in succession. 
The results obtained on the garden-soil seem to show that 
what is called " clover-sickness" cannot be due to the injurious 
influence of excreted matters upon the immediately succeeding 
crop. 
That the clover crop frequently fails coincident ly with injury 
from parasitic plants, or insects, cannot be disputed ; but it may 
be doubted whether such injury should be reckoned as the cause, 
or merely the concomitant and an aggravation of the failing 
condition. 
If, then, it be decided that the cause of failure is not destruction 
by parasitic plants or insects, nor injury from excreted matters, nor 
the shade of a corn-crop, and that it is to be looked for in ex- 
haustion of the soil, there will still remain several open ques- 
tions. Is it exhaustion of certain organic matters rich in carbon, 
of nitrogenous food, or of mineral constituents? Again, is 
there an actual exhaustion of the substances in question, or only an 
unfavourable condition of combination, or, so to speak, of soil- 
digestion of them, for the accumulative and assimilative require- 
ments of leguminous plants ? Or, is there only an unfavour- 
able distribution of them within the soil, considered in rela- 
tion to the extent and character of the root-range of the crops ? 
