APPENDIX. 163 



and moisture, which can in any way promote its 

 vigor during the first stages of germination. 



Silica to Stiffen Wheat Straw. It has been sup- 

 posed, and even taught, that the office of silica, 

 which occurs so largely in the straw of wheat and 

 other grains, was to stiffen it. With this idea, 

 fertilizers have been manufactured, containing 

 silica in a soluble form, for the pupose of affording 

 an extra supply to prevent the lodging of grain. 

 Such fertilizers are no longer offered for sale, as 

 no beneficial results were derived from them, but it 

 is still believed by many that silica is the main 

 cause of the stiffness of straw, and that the lodging 

 of grain on soil which is unusually rich in vegetable 

 matter is due to the lack of silica in such soils. 

 That there is no such lack of silica, however, in 

 any ordinary soils is easily proved by the fact that 

 scouring rushes which contain as high as ninety 

 per cent, of silica, grow in the deepest swamps, 

 where there is scarcely anything but vegetable 

 matter, obtaining all the silica they need in solu- 

 tion from the water which has dissolved it from 

 other plants and from soil over which it has passed. 

 Although silica or sand may appear insoluble, it is 

 in fact slightly soluble in ordinary rain-water, 

 especially when acted upon by the roots of plants, 

 and all the silica which plants need is readily 

 obtained from this source, even where the amount 



