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

Structure of Seeds 61Endosperm: Scanty, copious in Trigonella and Cyamopsis; cells in Trigonellaand Cyamposis thin-walled, mucilagenous.Seed coat in Arachis hypogaea is atypical for Faboideae, characteristic malpighiancells and hourglass cells are lacking and so are the special features of hilum.Seed coat of unlignified cells with cellulose thickenings, epidermis of short palisadeor squarish cells with thickenings on radial walls. Mesophyll and inner epidermisthin-walled enclosing vascular supply.Seed of bambarra groundnut (Vigna subterranean; syn. Vandezeia subterranea)has features similar to those of other Faboideae members.3.4.5 CUCURBITACEAE (FIGURE 3.8A TO F)(Singh, 1953; Singh, 1965, 1968; Singh and Dathan, 1972, 1973, 1974, 1990)External: Seeds medium to large, oval to ovate, ellipsoid or globose (Trichosanthesdioica); compressed or flattened, tumid or turgid, pointed or beaked at hilarend; white, pale or cream, brown to black, rarely red; smooth or sculptured with orwithout a distinct margin, winged in Luffa cylindrica; hilum inconspicuous; micropyleobliterated.Fresh seeds in Momordica and Trichosanthes enclosed in an envelope of placentalorigin (placental aril), usually red.Internal: Seed coat derived from outer integument only, generally consists offive identifiable zones: (1) seed epidermis, homocellular or heterocellular, cells large(epl) and small (eps), radially or horizontally enlarged; (2) hypodermis is a few tomany layered, thin- or thick-walled; when multilayered, it may be distinguished intotwo zones — outer zone of thin-walled cells and inner zone of thick-walled cells;in Luffa, cells of the innermost hypodermal layer are radially elongated, thick-walled,lignified and pitted; (3) main sclerenchymatous layer (e¢, the innermost derivativeof ovular epidermis), cells thick-walled lignified-macrosclereids (Luffa), oesteosclereids(Sicyos and Marah), or astrosclereids (Benincasa, Cucurbita, Cucumis,Citrullus, Trichosanthes, Lagenaria, and Momordica), (4) aerenchyma one or manylayered, cells stellate, thin-walled or weakly thick-walled, and (5) parenchyma orchlorenchyma, thin-walled cells with poor contents. The inner epidermis, which hassometimes been recognized as a distinct sixth zone, is indistinguishable from theadjacent cell layers.In mature seed, the outer three zones usually remain together while the innertwo zones — aerenchyma and parenchyma or chlorenchyma — detach from themain mechanical layer, forming two seed coats.Solitary seed in Sechium edule (chou-chou) is large, viviparous, seed coat leathery— cells of epidermis, hypodermis and the so-called main mechanical layerremain thin-walled and acquire abundant starch grains.Seed vascular supply traverses the inner layers in raphe and antiraphe, usuallyunbranched, branched and anastomising in Momordica, Trichosanthes, and Cyclanthera,three or more vascular bundles of ovary form ovular and seed supply inSechium and Sicyos.