Growth of Red Clover hj different Manures. 
{i^rowing in tlie experimental field to assimilate an increased amount 
of carbon from carbonic acid. The alkalies, potasli, cScc., have 
ceased to be as useful as manures for the Leguminous crops, as 
they were at the commencement of the experimental period ; yet, 
so far as the atmosphere is a source of constituents to these plants, 
its supplies must be the same now as formerly. The decline in 
the beneficial iniluence of the potash, >S:c., would aj)pe;»r, there- 
fore, to be connected with some defective condition within the soil. 
If we were to assume that the Leguminous plants required a 
certain portion of their organic food to be supplied to them in the 
form of certain organic compounds in the soil, it is evident that 
the beneficial action of the potash, ^Scc, would cease when these 
organic compounds were exhausted. On this assumption, too, it 
would seem intelligible, on the one hand, that an ordinary soil 
should require a considerable period of time after the growth of 
a Leguminous crop, t6 become again fertile for the same crop, 
and — on the other, that a garden soil, liberally manured with 
organic matter, perhaps for centuries, should support a con- 
siderable number of such crops in succession. 
It is further worthy of remark, in connexion with the beneficial 
action of the alkalies as manures for Leguminous crops, and with 
the supposition that these crops may require a portion of their 
organic food in the form of certain carbon compounds which are 
more complex than carbonic acid, that it is chiefly by the aid 
of tlie alkalies that the oi'ganic compounds of the soil are rendered 
soluble. On recently cleared lands in America, where there 
is such a great accumulation of vegetable remains, the em- 
ployment of ashes, and of gypsum, as top-dressings for Clover, 
has been attended with remarkable success. Vegetable ashes 
liave been found to be beneficial to the crop in this country also, 
which, independently of the mere supplij of potash, iS:c., may be 
partly due to the action above referred to. Gypsum, however, is 
by no means to be depended upon as a manure for Clover in this 
country. The action of gypsum has been very variously ex- 
plained upon high authority. The following distinct explanations 
are on record, namely : — that it serves as a supply of sulphuric 
acid— that it serves as a supply of lime — that it serves as a supply 
of sulphur — and that it serves for the fixation of ammonia. It is 
perhaps not less likely that its beneficial action may be con- 
nected with changes in the organic matters of the soil. M. Risler 
has indeed shown, that an aqueous solution of gypsum will take 
up more organic matter from soil, than will water. 
We are far from asserting that there is evidence enough to 
show that the failure of Clover, when grown too frequently on the 
same land, is altogether due to the want of a sufficient supply of 
certain organic compounds in the soil. At the same time, we 
think that the facts of horticultural and agricultural practice, as 
