Silica and Ash in Seeds of Cultivated Grains and Native Plants

Silica and ash contents and the depositional patterns of opaline silica have been determined in the seeds of 31 plant species. Included were 13 monocotyledons, eight dicotyledons and the seeds of eight common cereal grains. The cereal grains, except for Oryza sativa L. (3.2%) and Avena sativa L. (1.4%), were quite low in silica. The silica in these cereals was in the lemma. In seeds with high silica content it often makes up more than 50% of the ash. Silica in seeds occurs largely in the outer coating of the seed. Dicotyledon seeds tend to have less silica than those of monocotyledons. Energy-dispersive X-ray analysis shows that the distribution of the element silicon is clearly related to certain epidermal structures such as ridges, raised areas, trichomes and hairs. It also occurs in cell walls. Members of a specific plant family tend to have very similar silica depositional patterns in their seeds. Small amounts of K, S, Cl and Ca are also found in seeds. Light-microscopy studies show that the silica in the lemma of seeds such as Oryza sativa L. is deposited in cellular sheet-like structures with crenate edges. Silica in seeds also occurs in fibres and in other cellular structures (silica cells) that become phytoliths.