The endosperm and embryo that constitute the filial tissues of rice caryopsis are isolated from the maternal tissues by the absence of any symplastic continuity. Nutrients are transported to the endosperm through a single ovular vascular trace present on the ventral side of the ovary. Initially solute enters through the chalaza into the nucellar projection and then into the endosperm. At later stages transport occurs through the nucellar epidermis, centripetally towards the endosperm. The cell walls of the nucellar epidermis are provided with rib-like thicken ings. A comparison of grain-filling in C3 and C4 cereals suggests that rice has structural features allied to C3 cereals, such as wheat, but with significant differences.

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Horizontally-placed segments of Arena satira L. shoots show a negative geotropic response after a period of 30 rain. This response is based on cell elongation on the lower side of the leaf-sheath base (pulvinus). Triticum aestivum L., Hordeum vulgare L. and Secale cereale L. also show geotropic responses that are similar to those in Avena shoots. The pulvinus is a highly specialized organ with radial symmetry and is made up of epidermal, vascular, parenchymatous and collenchymatous tissues. Statoliths, which are confined to parenchyma cells around the vascular bundles, sediment towards the gravitational field within 10-15 min of geotropic stimulation. Collenchymatous cells occur as prominent bundle caps, and in Arena, they occupy about 30% of the volume of the pulvinus. Geotropic stimulation causes a 3-to 5-fold increase in the length of the cells on the side nearest to the center of the gravitational field. Growth can also be initiated in vertically-held pulvini by the application of indole-3-acetic acid, 1-naphthaleneacetic acid or 2.4-dichlorophenoxyacetic acid. 2.3.5-triiodobenzoic acid interferes with growth response produced by geotropic stimulation as well as with the response caused by auxin application. Gibberellic acid and kinetin have no visible effect on the growth of the pulvinus. Polarization microscopy shows a unique, non-uniform stretching of the elongating collenchymatous cells. Nonelongated collenchymatoug cells appear uniformally anisotropic. After geotropic "stimulation or auxin application, they appear alternately anisotropic and almost isotropic. Such a pattern of cell elongation is also observed in collenchyma cells of geotropically-stimulated shoots of Rurnex acetosa L., a dicotyledon.Abbreviations: 2.4-D=2.4-dichlorophenoxyacetic acid; GA3=gibberellic acid; IAA =indole-3-acetic acid; NAA = 1-naphthaleneacetic acid; TIBA =2.3.5-triiodobenzoic acid

Silica in plants can be stained by silver chromate, methyl red, and a colorless crystal violet lactone which are adsorbed by the silanol groups resulting in red-brown, red, and blue colors, respectively. Specialized silica cells in grasses can also be detected through polarization colors due to form birefringence. Silica in the bulliform and silica cells of rice leaves is amorphous and is made up of 1-2~nm particles aggregating into 2.5 X O.4-,um rods with oblique ends.

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