ON THE ROLE OF SILICA IN THE WHEAT-PLANT. 343 



V. Ovary multicellulfir. Zygote branches and gives 

 rise to numerous asci, in which spores are 

 developed. Lichens. 



2. Ovary has no special receptive portion and may be uni- 

 cellular or multicellular. Protoplasm of spermary does not 

 divide into sperms. Zygote branches, giving rise to one or 

 more asci. Erysifliect, Discomycetes. 



10.— ON THE ROLE OF SILICA IN THE WHEAT- 

 PLANT, IN DETERMINING A COMPARATIVE 

 IMMUNITY FROM THE ATTACKS OF THE 

 RUST FUNGUS. 



By Henry Trvon, of the Queensland Museum, Brisbane. 



It is well known that silica is one of the components of the 

 inorganic skeleton of the cell wall of plants, and that though this 

 is so, its total amount in any plant may vary to a large extent 

 without the normal structure of that plant being departed from, 

 and this is especially so in the case of cereals. But though this 

 variation, within certain limits, in the quantity of silica may 

 have little or no influence in enabling a plant to retain its 

 physical structure, it may to some extent determine its capacity 

 or otherwise for withstanding disease, and thus the opinion has 

 been expressed that wheats which are poor in silica are especially 

 subject to the attacks of rust, and more frequently than other 

 wheats, succumb to that disease. Mons. M. Gneymard, in 1859, 

 even went so far as to attribute to this deficiency in silica the 

 cause of the rust, at the same time stating that the wheat-plant 

 should contain as much as sixty per cent, of this mineral.* Again, 

 more than twenty years since (as we are informed in the Queens- 

 lander, of the 30th May, 1887) there was a pamphlet published, 

 by J. J. Moore, of Sydney, the title of which was "Rust in 

 Wheat." The theory pi'esented by the author was, that the 

 development of the disease was attributable in part to the deficiency 

 in silica — .such an important element in the straw. 



The reason which lead in either case to the expression of this 

 opinion, as to the influence of silica, is not forthcoming, but it was 

 probably founded on the observation that wheats in which this 

 mineral whs deficient, were more subject to rust than were those 

 in which it was largely represented as a constituent body. 



In the case of M. Gneymard, this view received confirmation 

 from M. Bouquet, an agriculturist of great experience, who 

 recorded as the result of his own observation that — in the 



• Comptes Rendus, 1859, xlix. p. 547. 



