248 PR. DAUBENY ON THE ROTATION OF CROPS, ETC. 



caused by the fibres of the roots insinuating themselves amongst them — owing to 

 water impregnated with carbonic acid, excreted by the extremities of the roots, 

 which may exert its solvent power upon the principles contained in the soil — and 

 owing to an imbibition, by the plants themselves, of the water surrounding them, 

 which would cause a general movement and circulation in the fluid contained in 

 all the portions of the soil contiguous. 



On the other hand, it would seem, that a due supply of these necessary ingre- 

 dients, already prepared and available for their purposes, would itself be likely to 

 favour the development of the parts of the vegetable, and thus to cause a larger 

 portion of such substances to be extracted from the earth, by the more vigorous 

 action excited within the secreting organs themselves. 



These effects are so connected together, that it is difficult to pronounce which of 

 them deserves to rank as the first link in the series. 



The only inferences, therefore, I could venture at present to deduce from the facts 

 which I have laid before the Society, are as follows : — 



1st. That it is quite consistent with the general tenor of the preceding facts and 

 observations, to maintain with Boussingault, that the falling-off" of a crop is de- 

 pendent upon a deficiency of organic matter proper to promote the nutrition of the 

 plants, as well as upon a failure of its inorganic principles ; not indeed that the 

 organic matter enters, as such, into the constitution of the vegetable, but that by its 

 decomposition it furnishes it with a more abundant supply of carbonic acid and am- 

 monia, which supply accelerates the development of its parts, and thus at once enables 

 it to extract more inorganic matter from the soil, and enables the soil to supply it 

 more copiously with the principles it requires. 



Hence, perhaps, in part, the advantage of intercalating the Leguminosse and other 

 fallow crops, which generate a larger amount of organic matter than the Cerealia, and 

 which thus serve to enrich the soil by what they leave behind them. 



2ndly. That it by no means follows, because a soil is benefited by manuring, even 

 though that manure may, as in the case of bones, guano, &c., derive its efficacy from 

 the phosphates it supplies, that the soil is therefore destitute of the ingredient in 

 question, since it may happen, that it possesses abundance of it in a dormant, though 

 not in an immediately available condition. 



In these cases, in which the agriculturist has been assured by the results of actual 

 analysis, that there is no real dearth of the principles essential to his crops in the soil 

 which he is cultivating, but where he has ascertained, either by the chemical mode 

 pointed out, or by an experience of the good effects brought about by manures, that 

 the principles in question are not in a state to become immediately applicable to the 

 purposes of vegetation, three courses appear to be open to him: — 



1st. To apply a sufficient quantity of the same materials in a state in which they 

 can be absorbed by the plants without delay ; 2ndly, to allow the ground to remain 

 fallow, by which expedient time is allowed for a further decomposition of its mate- 



