GYPSUM. 



323 



The mean o' these two experiments shows that the crop of white 

 clover on the ungypsed land being 100, that on the gypsed is 225 — 

 twice and a quarter more. 



The experiments of M. de Villele may be viewed as supplemen 

 lary oi complementary to those of Mr. Smith. They were per- 

 formed in the south of France, in accordance with the routine that 

 IS generally followed, viz : clover-hay, or sainfoin, previous to grain, 

 upon soils of considerably different nature, and with doses of gyp- 

 sum that varied from 8 to 3 on the same extent of surface. His 

 conclusions or crops are stated in the following table : 



The unquestionable fact of a mineral salt stimulating the growth 

 af certain plants in so remarkable a manner as to double and even 

 U) triple the usual quantities grown per acre, naturally aroused the 

 curiosity of mankind to inquire into and endeavor to discover the 

 cause Explanations in abundance have been proposed ; but so lit- 

 tle satisfactory in general, that I do not think myself bound to men- 

 tion them all. I shall limit myself, indeed, to two ; one proposed 

 I V Davy some time ago, and one advocated by Liebig very lately. 



Davy assumes that the plants of artificial meadows simply absorb 

 sulphate of lime. He assures us that he had found a large propor- 

 tion of this salt in the ashes of vegetables grown in soil which had 

 been treated with turf ashes abounding in the substance. He be- 

 lieved that the gypsum entered particularly into the constitution of 

 the woody fiibre. And it is not uninteresting to observe, that the 

 ulants which gypsum certainly favors in the highest degree, are of 

 very rapid growth ; and that in all probability they would find it 

 difficult to obtain the whole of the sulphate of lime they require from 

 ordinary or ungypsed soils within the period of their growth. Let 

 it not be forgotten, however, that if it be true that saline substances 

 are indispensable to the organization of plants, it is also true that 

 these substances can only be absorbed within certain limits ; a salt 

 the best calculated by its nature to aid vegetation, would become in- 

 jurious by its excessive proportion, did the water which moistened 

 the general soil contain too large a proportion of it in solution : if a 

 plant languishes when it has sot enough of one or other of its natu- 

 ral saline constituents, it also dies when furnished with the «aniSf 

 iubstance in excv,ss. 



