346 PROCEEDINGS OP SECTION D. 



this silicic acid passes into the insoluble state within the cell walls ; 

 but he does not, however, refer at all to the soluble alkaline 

 silicate. 



That silica is also taken up directly by the roots in a minutely 

 divided state, and by some process unrecognised by vegetable 

 physiologists, seems also probable in view of a discovery announced 

 by Prof. P. B. Wilson, of the Washington University, that 

 Diatoms, i.e., microscopic organisms whose pustules are almost 

 wholly siliceous, are present within the tissues of the straw of 

 wheat, grown under circumstances favourable for their obtainment, 

 and to adopt the title of his memoir on this subject, that " Silica 

 of grasses and other plants (are) carried up as diatoms or other 

 siliceous grains and not in a solution as soluble silicates.* In 

 this record of his researches. Prof. Wilson states that he found 

 generally that the silica in the ash of plants, obtained by slow 

 incineration, liad different properties from "silicates soluble in 

 acid or those decomposed with sodium and potassium carbonates," 

 and that its appearance showed that it had been assimilated in a 

 free state. Further, that the straw of wheat grown in infusorial 

 earth, contained under this circumstance siliceous matter wholly 

 composed of the siliceous shields of Diatomacese in their original 

 form and identical with those contained in this earth — the larger 

 discs only of the species being absent. The question of how these 

 siliceous grains do, as it seems they do, effect an entrance into the 

 plant-structure, through the medium of its roots, is not discussed 

 by Prof. Wilson, but it would seem to us that some light is thrown 

 upon the subject by the quite recent researches of H. Marshall 

 Ward, M.A., F.L.S., relating to the entrance of some germinal 

 elements of a particular fungus into the root hairs of the vetch, f 



We may next consider the value of the Darling Downs soils in 

 respect to their possession of assimilable silica. Are they rich 

 or poor in this desideratum of the properly constituted wheat 

 plant 1 Some light may be thrown on the subject by an examina- 

 tion of its soils, but it would seem that our immediate inquiry 

 will best be answered if attention is confined to wheat plants 

 raised there. What amount of silica then do they contain ? 



Unfortunately, however, we have no data which will supply this 

 information. The constitution of the straw of wheat raised in 

 tlie wheat-growing districts of the colony, and especially on the 

 Darling Downs, has not been made the subject of scientific in- 

 vestigation, but that the wheat raised in the latter district is poor 

 in silica is a very prevalent opinion. Thus, " A Farmer's Friend " 

 in the Queenslander, 30th May, 1887, states, " If any of your 

 readers will compare the wheat straw which they will remember 



* American Journ. Sc. 1876, xi. pp. 373-4. 



t Vide " The Tubercular Swellings in the Roots of the Leguniinosesa." Proc. R. Soc, 

 London, xlii., No. 255, p. 331. 



