142 TlMEHRI. 
keep pace with the requirements of the plant.* Defi- 
ciency of available silica is probably closely connected 
with the asthenia, (so prevalent in this colony) and other 
diseases of canef ; whilst encouraging results in culti- 
vating the plant have attended an increased supply of 
potash, according to experiments now being carried out 
in the French islands, and by Prof. HARRISON in Bar- 
bados. If, then, the large stores of silica and potash locked 
up in the soil can be made more available by gypsum, 
it would be more economical to employ it for the purpose, 
being a cheap substance, than to supply potash salts and 
soluble silica, which are relatively much more expensive. 
The property of gypsum in promoting nitrification 
would only be of service when organic nitrogenous 
* In connexion with this point it may be of interest to give the following 
extratt from " A General System of Botany" by Le Maout and 
Decaisne, translated by Mrs. Hooker 1873, pp. 144-145: "Alkalies 
and especially potash, when mixed with soil, are rendered soluble by 
the addition of sulphate of lime as Deherain has proved. Since the 
sulphate of lime changes the salts of potash into sulphate of potash it 
has been supposed that the greater solubility of potash after being thus 
treated is attributable to this transformation. This hypothesis has not 
yet been practically proved, and we do not know whether the sulphate 
afts chemically on the potash or whether its effefts are purely physical, 
the objeft being to liquefy the soluble salts, to preserve them from the 
absorbent a6tion of the earth, and to facilitate their absorption by the 
roots of the plant. But whatever be the explanation, this property of 
sulphate of lime proves the advantage of adding it to the soil in which 
leguminous fodders are cultivated (Trefoil, Lucerne, Sainfoin,) of which 
the ashes are rich in potash." 
f See Report on Sugar Cane Disease in the Mary River District, 
Queensland by Prof. Liversidge. {Sugar Cane, 8, 544). The ash of 
healthy Rappoe cane contained 51.45 0/0 silica and of the diseased 
only 13.6 0/0. The ash of healthy and diseased Troebce contained 22.82 
and 1 1.36 0/0 respectively. 
