Ash and silica contents and depositional patterns were determined for different tissues of 11 plants growing in the southeastern and central parts of the USA. Silica content was high in the leaves, sheaths and inflorescences of the grasses studied, especially high in leaves of Polymnia uvedalia L., which are also high in calcium. Calcium deposition was largely in trichomes and in veins of the leaf. Energy-dispersive X-ray analysis showed that the distribution of the element silicon is closely related to certain epidermal structures such as ridges, cell walls, rows of irregularly shaped structures lying lengthwise along the leaf, dumb-bell shaped structures and trichomes. These structures also correspond to the phytoliths left behind after decay of the plant. The C3 grasses differed from the C4 in that they showed oval structures and produced correspondingly oval phytoliths. Silicified trichomes (particularly in the C3 grasses) and long, narrow, silica fibres were common in the inflorescences of the grasses studied. These sharp particles could be irritating to oesophageal and other tissues. Similar fibres in other grasses have been implicated in certain cancers. High silicification of the inflorescences structures might afford protection for the seed, as reported for other grasses. Key words: C3 and C4 grasses, silica and ash content, scanning electron microscopy, energy-dispersive X-ray analysis, silicon distribution, spectra of elements in plants, trichomes, silica fibres, phytoliths