92 
EOTAL HORTICITLTXJIIAL SOCIETY. 
These various points cannot be considered in detail within 
our present limits ; but a few brief observations may be made in 
reference to them by way of explanation and suggestion. 
The results obtained on the garden-soil are, of course, con- 
sistent with the supposition that there was in the field-soil a want of 
some of the ultimate elements of the crop. They are also con- 
sistent with the assumption that it is not merely requisite that 
the constituents should be present in the state of combination 
and of distribution available for other descriptions of crop, but 
that it is essential for the healthy development of the clover- 
plant, that the constituents should have undergone a certain 
digestion, so to speak, within the soil ; or that certain consti- 
tuents should have become more distributed than is necessary 
for the cereal crops. On either supposition the result may be 
dependent on the proper supply of carbon, of nitrogen, or of 
mineral constituents. Thus, in garden-soil, liberally dunged for 
centuries, there would be a great accumulation of all constituents. 
A large amount of both carbon and nitrogen compounds would 
have undergone considerable, if not as complete change as could 
take place within the soil ; and their products, as well as mineral 
constituents, would be widely distributed. 
Although, taking the whole period, carbon has been removed 
in the crops from all the plots in larger quantities than it has 
been supplied to them in manure, experience with other descrip- 
tions of crop would not lead to the supposition that the failure 
could be due to a deficiency of that constituent provided it were 
taken up by the Leguminosse exclusively as carbonic acid, yielded 
by the atmosphere, or by the decomposition of organic matter 
within the soil. If, however, it were the case that some plants, 
clover, for example, required for healthy development at certain 
stages of their growth a portion of their carbon to be presented 
them in other compounds — organic acids more complex than 
carbonic acid, in combination, it may be, with ammonia, or with 
fixed bases — we could then easily understand that, under ordi- 
nary circumstances, a certain period of time might be requisite 
for the formation and accumulation of a sufficient amount of the 
compounds in question. It would also be intelligible that there 
should be a great accumulation of such compounds in the soil 
where dung had been liberally used for centuries. A fact of 
another kind, which is at any rate consistent with the view here 
assumed, is, that the ashes of the Leguminosse we cultivate con- 
