On the function of silica in the nutrition of cereals.―Part I

The presence of silica in plants was first demonstrated by the analyses of De Saussure, who pointed out that the Gramineæ were particularly distinguished by the large proportion of this constituent present in their ash. Liebig, who classified plants as “silica plants,” “lime plants,” and “potash plants” according to the predominance of one or other of these constituents in their ash, in accordance with his “mineral theory,” regarded the silica as a necessary element in plant nutrition. This view led Way to introduce as a cereal manure a rocky material derived from the Upper Greensand near Farnham, which contained a considerable proportion of silicate easily soluble in acids. But when Sachs succeeded in maturing maize plants in water cultures containing no silica, whereby the proportion of silica in the ash of the mature plant was reduced from the normal 20 per cent. or so to as little as 0·7 per cent., it became evident that silica could no longer be placed in the same category as phosphoric acid and potash as essential elements of plant nutrition, and Jodin raised four successive generations of maize in water cultures without any supply of silica beyond that contained in the original seed. Other investigators again showed that the stiffness of cereal straw, which had been attributed to the presence of silica, depends on the development of the internodes under the influence of such factors as illumination and exposure.