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

Structure of Seeds 57Endosperm: One- or two-layered, cells of outer layer contain aleurone grains.3.4.2 MALVACEAE (FIGURE 3.5A TO H)(Ramchandani, Joshi, and Pundir, 1966; Joshi, Wadhwani, and Johri, 1967; Kumarand Singh, 1990, 1991)External: Seeds usually compressed, reniform with central notch or subglobose(Abelmoschus esculentus) or pyriform (Gossypium); usually brown to black; smooth,rough, rugose, or hairy (Gossypium and some Hibiscus spp.); hilum flush ordepressed within the notch; micropyle inconspicuous; obliterated; stomata on seedsurface, particularly at the chalazal end.Internal: Seed coats two, exotegmic, differentiated into five or more zones: (1)seed epidermis, composed of thin-walled horizontal cells covered with thin cuticle,in Gossypium cells form lint as well as fuzz, sparse hairs in others; hairs are simple,one-celled or septate, thin-walled or lignified, hair bases are thick-walled; (2) outermesophyll, one or more layers of outer integument, thin-walled, in Gossypiumdifferentiated into an outer zone of pigmented cells and an inner of colorless cells;cells of inner epidermis inconspicuous, rarely with calcium oxalate crystals (Hibiscuscalycina); (3) palisade or macroscleroid layer, thick-walled, lignified, light line areain the outer half of cells, the layer formed by outer epidermis of inner integumentand is the main mechanical layer —seed coat exotegmic; (4) inner mesophyll usuallymulti-layered and differentiated into two zones: a pigmented zone of outer layersof small, thin-walled and tannin-pigmented cells and a colorless zone of thin-walledcells; (5) fringe layer, inner epidermis of inner integument, cells longitudinallyelongated, thick-walled with pits on radial walls and pigmented contents. In Gossypiumcells of inner mesophyll possess compound starch grains.The vascular supply is prominent and terminates at the chalaza below a tanniferouspad.Embryo: Peripheral, large, often curved, cotyledons two, foliaceous, folded orconvoluted.Endosperm: Scanty or one- or two-layered around the embryo, five- or sixlayeredat the micropylar and chalazal ends in Gossypium, also present between thefolds of cotyledons. The cells of endosperm and embryo are rich in oil and proteins.Cotton seed contains the alkaloid gossypol.3.4.3 LINACEAE (FIGURE 3.6A, B)(Boesewinkel, 1980, 1984)External: Seed small, flat or flattish, elliptic or elliptic-ovate, pointed at oneend; smooth, lustrous; yellow to brown; hilum inconspicuous, micropyle obliterated.Internal: Seed coats two, exotegmic; outer coat two-layered, epidermis of short,radially elongated cells with stratified mucilage deposits, cuticle thin, plicate, innerlayer parenchymatous, inner coat, epidermis formed of tangentially elongatedfibrous, thick-walled, lignified cells forming the main mechanical layer (exotegmic);mesophyll of crushed cells, inner epidermis — cells rectangular, thick-walled, pitson radial walls, tanniferous. Vascular supply terminates at the chalaza.