388 Dr. Daubeny's Lines of Inquiry 



effect of phosphate of lime, when derived from bones, or from 

 a rock possessing the same chemical constitution, but a differ- 

 ent mechanical texture? 



I am inclined to attribute to adhesive attraction more influ- 

 ence than is commonly ascribed to it, and believe that the 

 same substance, which under ordinary circumstances is totally 

 incapable of entering the vessels of a plant, may be absorbed 

 by it when its particles are kept apart, and the force of their 

 mutual affinity diminished, owing to the interposition of those 

 of some foreign matter. The superior fertilizing agency of 

 certain species of limestone to others, is perhaps dependent 

 upon this cause. 



It might therefore be interesting to manure the land with 

 lime obtained from the harder descriptions of limestone and 

 from the softer ones — from one sort destitute of organic mat- 

 ter, and from another composed of it; or with bones and with 

 the phosphorite of Estremadura. The fertilizing influence of 

 a comparatively small dressing of phosphate of lime treated 

 with sulphuric acid seems to show, that in the ordinary con- 

 dition in which bones are used as a manure, the cohesive at- 

 traction, which binds together their particles, is but slowly 

 overcome by the decomposing agents to which they are sub- 

 jected. 



Another set of inquiries will relate to the theory of rotations 

 and of fallows, subjects on which our present knowledge is 

 purely empirical, and therefore imperfect and unstable. 



It remains, for instance, to be seen, what may be the differ- 

 ence between the fertility of a soil exhausted by bearing a suc- 

 cession of the same or of different kinds of crops, without being 

 in the mean time refreshed by manure. When the latter is 

 subsequently applied to both, will the one on which various 

 crops have been grown recover itself sooner than that which 

 has received the same throughout ? Should the latter point 

 be established, it would lend some support to DeCandolle's 

 theory of vegetable excretions, and a new subject of inquiry 

 would then present itself, namely, how long do these excre- 

 tions remain in the ground without becoming decomposed, 

 and thereby losing their deleterious properties, and how far 

 may their decomposition be accelerated by artificial means ? 



The above may serve as examples of the kind of researches, 

 which might be undertaken on an experimental farm, but 

 which can hardly be expected to be elucidated in the ordinary 

 routine of farming — others more especially relating to the soil 

 may be pointed out, which come under the same category. 



Thus it remains to be ascertained whether phosphoric acid 

 is generally present in the soil — whether its quantity is pro- 



