456 



Messrs. A. D. Hall and C. G. T. Morison. [Dec. 22, 

 Table I. — Percentage of Silica in Ash. 



Si0 5) 



per 

 cent. 



(Rotham steel mean) 



Wheat straw 



» grain 

 Barley straw 



„ grain 

 Oat straw 

 „ grain 

 Eye grass (Lolium perenne) 

 Maize (whole plant) 

 Sugar cane 



(Wolff, mean) 



62 

 

 46 

 18 



46 

 36 

 26 

 43 

 50 



Hops, leaves (Wolff, mean) 



„ cones ,, 



Beech leaves „ 



Larch needles ,, 



Calamus Rotang (Wolff, 1 anal.).. 

 Bambitxa arundinacea 

 Sphagnum pulustre 

 Pteris aquilina 

 Equisetum arvense 

 Erica Tetralix 



Si0 2) 

 per 

 cent. 



21 -1 

 17 -2 

 31 -0 



22 -5 

 68 -0 

 28 -3 

 61 -8 

 43 -7 

 41 -7 

 48-4 



Owing to the inevitable presence of external dust and dirt upon plant 

 material before analysis, it is almost impossible to say whether the small 

 amounts of silica found in the ashes of many other plants are accidental or 

 inherent. 



But while it has been demonstrated that silica is not essential to the 

 nutrition even of the cereals, it is hardly likely that a material present 

 to the extent of 60 per cent, of the mineral constituents, as in the ash 

 of wheat-straw, can be wholly without use in the economy of the plant. 

 The only experiments, however, which throw any light on its function 

 appear to be those of "Wolff and Kreutzhage.* These investigators grew 

 oats in culture solutions of the type usually described as complete, but 

 further divided into three series, receiving soluble silica in considerable 

 quantity, in a small quantity, and not at all. They observed that while the 

 total growth was not much increased by the presence of silica, the pro- 

 portion of grain formed was considerably raised, a precisely similar effe-ct 

 to that brought about by an addition of phosphoric acid to culture solutions 

 deficient in that element. Hence they concluded that the action of silica 

 and of phosphoric acid were in some way related, the former acting, 

 however, indirectly on grain formation by promoting the migration of the 

 food materials. 



With this exception the possibility that silica plays any part in plant 

 nutrition appears to have been ignored, just as its practical use in the 

 manuring of cereals has been discontinued. Observation, however, of some 

 of the plots at the Eothamsted Experimental Station, which have long been 

 subjected to a manuring with soluble silicates, seemed to show that the 

 question of the function of silica required further consideration, and an 



* 1 Land. VersuchsstationeE,' vol. 30, 1884, p. 161. 



