Gypsum as a Cane Fertiliser. 135 
sainfoin, containing 34 lbs. of lime ; and of Italian rye 
grass, containing but 14 lbs. of lime ; yet, it is powerless 
to augment an average crop of turnips which requires 
go lbs. of lime, or of a similar crop of carrots requiring 
no less than 197 lbs. of lime. 
That the action of gypsum could not be altogether 
attributed to the sulphur or sulphuric acid supplied by 
it, was also proved by similar facts adduced by Way, 
who finally states that " the crops which are most 
benefited by the application of gypsum contain far less 
of either lime or sulphuric acid than those upon which 
this manure produces no kind of effect." While ad- 
mitting that gypsum may exercise the function of 
absorbing and retaining ammonia, Way considered its 
action in this respect superfluous, because he had in- 
disputably proved that <l soils have a power, quite inde- 
pendent of the presence of sulphate of lime, of retaining 
the carbonate or any other salt of ammonia that may be 
brought in contact with them." 
More recent observers have sought in other directions 
for an explanation of the action of gypsum. Thus, an 
Italian chemist, COSSA, ascertained that water con- 
taining gypsum formed a more powerful solvent of the 
plant constituents of soil than water free from it. Water 
is able to take up about T ^_ of its weight of gypsum, and 
this solution when allowed to remain in contact with the 
finely ground rocks, which go to form clay, dissolved out 
of them from two to three times as much potash, 
lime &c, as pure water is capable of doing, and thus 
probably aided the plant in obtaining its proper supply 
of mineral matter. 
But by far the most important addition to our know- 
