on Permanent Meadoio Land. 
237 
acre, in the average annual produce of the unmanured land. Where 
an enormous amount of organic matter, rich in carbon, was supplied 
in the form of sawdust, little or no increased assimilation of carbon 
took place ; where a still larger quantity was employed in the 
form of farm-yard manure (in admixture, therefore, with other 
active manurial matters), there was a considerable increase in the 
assimilation of carbon. But, under these circumstances, it is 
doubtful whether the farm-yard manure itself was the source of the 
increased amount of carbon fixed, or, at any rate, whether its 
supply of that substance (in the form of carbonic acid or other- 
wise) has been at all essential. 
Thus, it was by means of mixtures of mineral manures and 
ammoniacal salts, without the direct supply of any carbon, 
that the greatest increased assimilation of that substance was 
obtained. For instance, on plots 10 and 13, there was an average 
of about 1 J tons of increase of dry substance per acre, per annum, 
by the use of the mixed mineral manure and ammoniacal salts. 
This amount of gross dry increase represents an increased assimi- 
lation of carbon, by about 12cwts. per acre per annum, without 
the supply of any in the manure. To this enormous extent, 
therefore, have these now-carbon-yielding manures enabled the 
plants, either by their roots or their leaves, to draw that element, 
so essential for the maintenance of the respiration, and for the 
fattening of our animals, from the atmosphere : — into which, 
in the course of the ever-constant revolutions of organic nature, 
it had been emitted by the combustion or decomposition of the 
products of former vegetation, or by the respiration of animals 
fed on former crops : — and into which, it is destined to be returned 
by the same means, as the resource of future vegetable growth. 
It was seen, how unavailing were mineral manures alone ma- 
terially to increase the growth of the Graminaceous hay-plants. 
That is to say, by their supply alone, these plants were not 
enabled to assimilate an increased amount of either nitrogen or 
carbon from natural sources. Nor did the supply of one of these 
elements — carbon — enable the plants to draw from natural 
sources an increased amount of the other element — nitrogen. On 
the other hand, provided there were a sufficiency of the necessary 
mineral constituents, the supply of the element nitrof/en, in an 
available form of combination, increased enormously the assimi- 
lation of the atmospheric constituent carbon. It may be re- 
marked in passing, that a very similar result is observed when 
nitrogenous manures are employed for the Graminaceous crops of 
our rotations. Not that no other crops are found to assimilate 
an increased amount of carbon without its supply in manure, 
when they have a sufficiency of mineral constituents and avail- 
able nitrogen within the soil. But compared with others, the 
