Proceedings of the British Association. 319 



to name electrogen, must be admitted into the list of supposed 

 elements: that it was ?iot a union of an electrolytic compound 

 whose action was unknown; and that probably it exists in com- 

 bination in various forms of matter, which at present are consid- 

 ered elementary, but which in reality are not so, 



A paper on manures considered as stimiilajits to vegetation, 

 was communicated by Dr. Daubeny. The author discusses the 

 question as to ihe sense in which manures can be considered to 

 act as stimulants to plants. It is evident that if the term stini' 

 ulus be understood in an acceptation similar to that in which 

 it is employed with reference to the animal economy, it ought to 

 be confined to bodies, which by their presence, assist in promot- 

 ing the secretion and assimilation of the nutritious materials pres- 

 ent, and ought not to include such as themselves afford ma:terials 

 for secretion. Thus salt and other condiments do not themselves 

 nourish the animal ; but by their presence, induce its secreting 

 surfaces to assimilate more readily the substances presented to 

 them. Now, it becomes a fit subject for inquiry, whether ma- 

 nures operate in the former manner or in the latter ; and likewise 

 whether the fact, that certain of them act less beneficially at sub- 

 sequent periods of their application than they did at first, admits 

 of being explained on the recognized, principle that " stimuli lose 

 their full effect upon living matter when frequently repeated." 

 Dr. D. adduced several facts which led to the inference that the 

 nitrates of soda and of potassa operate favorably upon certain 

 crops by communicating to them nitrogen ; and the reason why 

 these salts sometimes have appeared to leave the land in a worse 

 condition than before their use, is not owing to their being stim- 

 uli, and therefore amenable to the law above quoted ; but is be- 

 cause the free supply of nitrogen afforded by the decomposition 

 of the nitrates, had caused the plant to absorb a larger portion of 

 those other ingredients, such as phosphate of lime, silicate of po- 

 tassa, &c., which are present only in a limited quantity in the 

 soil, thus tending to exhaust it of these materials, and causing 

 thereby an inferior crop to be produced on the following year. 

 Now, though it may be true that the nitrates in this manner in- 

 directly stimulate the vital energies of the plant, yet it was con- 

 ceived that the term stimulus had better be abandoned with ref- 

 erence to such cases, as its adoption might lead to an erroneous 

 impression in the mind of the farmer with respect to the proper 



