EMPLOYED IN AGRICULTURE. 157 



latter is so much more accessible, and consequently, beyond 

 all comparison, more economical. The oi)inion is based 

 u[)on a series of experiments, wliicb tend to sliow that clover 

 treated with gypsum not only contained more sulphate of 

 lime than it had without it, but also a larger proportion of 

 lime in other states of combination — a very natural conse- 

 quence, in my opinion, supposing- the absorption of the 

 quantity of gypsum which was cong'enial to its organization 

 had invigorated the system of the plant, and thus had 

 enabled it to draw more larg'ely from the soil than it other- 

 wise could have done. 



The converse hyi)othesis experienced by Professor John- 

 ston seems hardl}' consistent with the fact that gypsum is 

 better adapted for leguminous plants than for cereals, inas- 

 much as the latter, according- to Boussing-ault, yield quite as 

 much sulphur on analysis as the former. 



With reg-ard to the remaining- hypothesis, propounded by 

 Sir Humphry Davy and by Baron Liebig, it is probable that 

 both the causes assigned by these two j^hilosophers may 

 have a share in the virtues which belong- to gypsum as a 

 manure. 



All authorities concur in asserting- that those crops which, 

 contain the largest amount of sulphate of lime in their com- 

 position are most benefited by the ap})lication of the sub- 

 stance in question ; and, indeed, even the experiments of 

 Boussing-ault, which are alleged in opjiosition to this theory, 

 evince that clover treated with g-ypsum contained in its 

 ashes more of this ingredient than it had done under other 

 circumstances. 



But there is one mode of applying- g-ypsum much prac- 

 tised on the Continent, and also in the United States of 

 America, which seems to im})ly a distinct mode of opera- 

 tion from the other. This is the })ractice of scattering- 

 g-y[)sum in fine powder over the leaves of the crop when 

 just rising- above the ground, which is stated to invigorate 

 the stem and leaves, and even to extend its beneficial in- 

 fluence to the roots themselves. 



This circumstance would seem to point to some function 

 of the substance employed in absorbing- ammonia, and thus 

 bringing this highly important substance into immediate 

 contact with the parts which are most ready to assimi- 

 late it. 



M. Boussing-ault objects to this view of the subject on 

 grounds that appear to me exceed ngly inconclusive. He 



