ACTION OF GYPSUM ON CLOVER NOT KNOWN. 345 



of magnesia, were as G : 8 ; the ash of the clover pro- 

 duced by sulphate of lime contamed a little more than 

 8 lbs., and that from the sulphate of magnesia G lbs. On 

 the plot dressed with gypsum the clover plant found a 

 larger total quantity of sulphuric acid than on the sulphate 

 of magnesia plot, and absorbed a correspondingly larger 

 proportion. But this additional quantity of sulphuric 

 acid absorbed did not increase the amount of produce ; 

 on the contrary, on the plot manured with sulphate of 

 magnesia, which had received less sulphuric acid than the 

 gyi^sum plot, the amount of vegetable matter was 8 per 

 cent, higher than on the latter. 



These facts show that we are still in the dark about the 

 action of g}^3sum ; and it will yet require a great many 

 and most accurate observations before we are likely to 

 arrive at a satisfactory explanation. 



So long as the notion was generally entertained that 

 plants derived their food from a solution, the effects of a 

 soluble salt upon vegetation could, of course, be attri- 

 buted only to the constituents of that salt. But now we 

 are aware that the earth itself performs a special part in all 

 the processes of nutrition ; and there might, therefore, be 

 grounds for supposing that the action of gypsum upon 

 arable earth, or of the latter upon the former, might 

 furnish a key, to some degree at least, to explain the effect 

 of gji^sum upon the growth of clover. A series of ex- 

 periments made by me upon the alterations which a satu- 

 rated solution of gypsum in water undergoes in contact 

 with different arable soils, give very remarkable results, 

 wliich I will now state, without venturing to draw any 

 defmite conclusions from them. 



I found that a solution of gj^psum in contact with all 

 the arable soils which I used, underwent decomposition, 

 part of the hme separating from the sulphuric acid, and 



