STUDIES OF SILICA IN OAT PLANT .4. SILICA CONTENT OF PLANT PARTS IN RELATION TO STAGE OF GROWTH SUPPLY OF SILICA AND TRANSPIRATION

Oat plants, Avena sterilis L., were grown on soils in which the concentration of monosilicic acid in the soil solution, that is the level of supply of silica, ranged from 7 to 67 ppm SiO2. Analyses at intervals throughout the growing period showed that the level of supply affected the amount and concentration of silica in the plant but not the pattern of its distribution among the parts. At maturity the caryopsis contained only 0.5 to 0.8 per cent of the total silica in the tops while the other parts of the inflorescence contained 40.7 to 41.3 per cent. The leaves (blade and sheath) contained 42.5 to 45.0 per cent of the total silica and the stems contained 7.8 to 10.9 per cent; the remainder was present in small sterile tillers. The concentration of silica in the dry matter was highest in the palea, lemma glumes, awn, and leaves. Among the leaves, the flag leaf had the highest silica content, both in terms of concentration in the dry matter and amount per leaf. The distribution of silica along a leaf followed a hyperbolic curve, the concentration being highest at the apex and lowest at the base of the blade. The chemistry of silica and the pattern of its distribution in the tops suggest that monosilicic acid and water move concomitantly in the transpiration stream and that solid silica is deposited in greatest quantities in those parts and regions from which water is lost in greatest quantities. © 1968 Martinus Nijhoff.