Histopathology of Seed-Borne Infections - Applied Research Center ...

66 Histopathology of Seed-Borne InfectionsInternal: Seeds thinly albuminous, seed coat exotestal; epidermal cells radiallyelongated and those at the edges larger, forming ridges, crystalliferous (calciumoxalate crystals), crystals in outer part of cells in Sesamum indicum and in innerregion in S. radiatum; mesophyll — four to six layers, thin-walled, compressed;inner epidermis — endothelium in developing seed, cells unspecialized and boundon inner side by cuticle.Embryo: Erect, axile, broadly spatulate, cotyledons two, multi-layered, hypodermison adaxial side of palisade cells, remaining layers of isodiametric cells;reserve food material, oil and aleurone grains.Endosperm: Two to five layers, epidermis covered by cuticle, cells thin-walled,oil and aleurone grains as reserve food material.3.4.8 SOLANACEAE (FIGURE 3.10A TO K)(Saxena and Singh, 1969; Saxena, 1970; Vaughan, 1970; Sharma, 1976)External: Seeds small to medium, flattened and subcircular or discoid (Lycopersicon,Solanum and Capsicum), minute and globose, subglobose or cubical (Nicotiana);white to yellowish, brown-black; smooth, reticulate or hairy; hilum indiscoid seeds marginal in notch, but in globose and cubical seeds subterminal andflush; micropyle inconspicuous.Internal: Seed coat one, exotestal, seed epidermis main mechanical layer, cellsradially elongated with inner tangential and radial walls thickened, thickening heavyat base and tapering outwards, lignified, outer tangential wall remains thin (Lycopersiconand some Solanum spp.); cells flattened with rodlike thickenings on radialwalls emerging from inner tangential wall (Capsicum, some Solanum spp.), epidermalcells with radial and tangential walls thickened, lumen full of pigmented contents(Nicotiana); mesophyll present or absent, when present cells thin-walled, compressed,if multi-layered those in outer zone distinct (Capsicum); inner epidermis(endothelium) — cells small, narrow, thin-walled with striate or reticulate thickenings,full of pigmented material.Note: Freshly harvested seeds in Lycopersicon and Solanum are enclosed in asucculent sac (arillode of placental origin). It loses water on exposure to the atmosphere,reduced to a thin membrane. The dried arillode and the outer tangential wallof seed epidermis get detached, and the thick radial walls assume the appearanceof hairs, silky outgrowths or rodlike fibrous thickenings. Corner (1976) called themspurious hairs and Rick (1978), pseudohairs. No true hairs occur on seeds ofSolanaceae.Embryo: Axile straight, bent or curved (Nicotiana), coiled, annular (Capsicum,some Solanum spp.), spirally coiled with tips incurved (Lycopersicon, some Solanumspp.), coiled with tips recurved (Datura spp.); cotyledons two, flat or folded, hypocotyledonaryroot axis well developed, cells with oil and aleurone grains.Endosperm: Five- or six-layered; in seeds with coiled embryo with commahead and comma stem; cells thin or thick-walled, parenchymatous, reserve foodmaterial as oil and aleurone grains.