124 LETTER-FILES OF S. W. JOHNSON 



is "preferred by plants." Unfortunately for this "doctrine 

 of a theorist, ' ' the first cargoes with which the published 

 experiences have been made, and upon which the reputation 

 of this manure has been built up, appear from the analyses 

 of Torrey, Gale and myself, to have been nearly free from 

 sulphates to have been in fact, nearly pure phosphate of 

 lime ! In all the numberless trials on record made with the 

 special object to learn the value of various fertilizers, there 

 has, as yet, been found no jot of evidence that any "natural 

 combination" of two fertilizers exceeds an artificial one in 

 its effects, and your correspondent must adduce some evi- 

 dence, some stubborn fact, to sustain his view; for neither 

 science nor experience is to be convinced by his assurance 

 that the roots of plants, if questioned, would probably tell 

 the farmer that they prefer American guano, because of the 

 "natural combination" of phosphate and sulphate of lime. 

 The fineness of the American guano would be certainly in its 

 favor, were it chiefly a phosphate of lime, but it is wrong to 

 assert that such fineness is any advantage in case of a sulphate 

 of lime, or that the roots of crops have to "struggle" to obtain 

 sustenance from the coarser particles of Nova Scotia plaster, 

 which, as sold for agricultural purposes, has, for the plant, a 

 high degree of solubility. 



That American guano has in many cases equalled and 

 excelled Peruvian guano is very likely true for simple and 

 obvious reasons, independently of the testimony of farmers. 

 That plaster, common salt, leached ashes and other fertilizers, 

 have equalled and excelled Peruvian guano is also true. "We 

 cannot, however, claim for the last named substances a supe- 

 riority over Peruvian guano, nor can "D. R. S." claim such 

 superiority for American guano. It is a principle recognized 

 by all thorough agriculturists that whatever a soil or crop 

 needs is the most valuable application to it; it may be phos- 

 phates, it may be sulphates; it may be salt, or water or sun- 

 shine. It is well known that the repeated and exclusive use 

 of Peruvian guano, of plaster, of salt, of lime or of any one 



