324: SALT, NITRATE OF SODA, SALTS OF AMMONIA, ETC. 



compared with the enormous increase in the weight of 

 the stems, and a not inconsiderable one in the weight 

 of the leaves, we find no increase of flowers, and con- 

 sequently also none of seed (Pincus). These most care- 

 fully conducted experiments confirm the general rule, 

 that wherever external causes favour the developement 

 of some organs, it can only be eifected under like con- 

 ditions of the soil, at the expense of other organs, and 

 that in the case of clover, as in that of the cereals, in- 

 crease of straw is attended with decrease of seed. (For 

 further details of these experiments, see Appendix J.) 



As the substitution of magnesia for lime, in the ex- 

 periments now described, led to an increase of the 

 clover crop, it may be safely assumed that in cases 

 where gypsum is found to be favourable to the growth 

 of clover, the cause must not be sought for in the lime, 

 although it is very often found that many fields will 

 grow clover only after a copious dressing with hydrate 

 of lime. For we know also that gypsum promotes the 

 growth of clover on many fields naturally abundant in 

 lime ; and since arable soil has the property of absorb- 

 ing ammonia from the air and rain-water, and fixing it 

 in the same or even a higher degree than salts of lime, 

 there is only the sulphuric acid left to look to for an 

 explanation of the favourable action of gypsum upon 

 the growth of clover. 



But the experiments of Pincus clearly demonstrate 

 that the crops obtained by manuring with* the sulphates 

 bear no proportion whatever to the quantity of sul- 

 phuric acid supplied in them to the field. 



The quantities of sulphuric acid severally contained 

 in the two sulphates used were 30*12 Ibs. in the sul- 

 phate of magnesia, and 44*18 Ibs. in the sulphate of 

 lime, which is as 6 : 8*8. The quantities of sulphuric 

 acid in the two crops obtained severally by sulphate 

 of lime and sulphate of magnesia, were as 6 : 8 ; the 

 ash of the clover produced by sulphate of lime con- 

 tained a little more than 8 Ibs., and that from the sul- 

 phate of magnesia 6 Ibs. On the plot dressed with 

 gypsum the clov*er plant found a larger total quantity 



