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

Structure of Seeds 553.3.2 SEED COAT AND PERICARPThe protective covering of seed is the seed coat in true seeds, pericarp, or bracts inone-seeded fruits. The seed has a main mechanical layer, which, as mentioned inChapter 2, differentiates in the outer or the inner integument. Corner (1976) classifiesdicotyledonous seeds into testal or tegmic, depending on whether the main mechanicallayer has differentiated into the outer or the inner integument. Each category issubdivided on the basis of the place of differentiation of the main mechanical layerinto exotestal, mesotestal, and endotestal, and exotegmic, mesotegmic, and endotegmic,respectively. Each subcategory is further divided into two or more types onthe basis of the nature (shape and size) of cells in the main mechanical layer.Corner (1976) did not consider unitegmic seeds (seeds formed from unitegmicovules) in his classification, but he remarked that these can be called exotestalbecause the seed coat develops in an exostestal manner in these ovules. The seedcoat in monocotyledons also has a main mechanical layer, and Corner’s concept canbe readily extended to the structure of the seed coat in this group as well (MaheshwariDevi et al., 1994).The pericarp in caryopsis, cypsils, cremocarp, achene, and utricle is also characterizedby the presence of mechanical (sclerenchymatous) layers and the presenceof cuticle on the surface (Lavialle, 1912; Borthwick and Robbins, 1928; Bradburyet al., 1956a,b; Gupta, 1964; Bechtel and Pomeranz, 1978; Zeleznak and Verriano-Marston, 1982; Kaul and Singh, 1982).For detailed information on seed coat structure the reader should refer toNetolitzky (1926), Singh, (1964), Vaughan (1970), and Corner (1976). The Structureand Composition of Foods, Vols. 1 to 4 (Winton and Winton, 1932–1939), givedetailed information on the microscopic structure of various parts, namely the seedcoat and pericarp, embryo, and endosperm and perisperm of grains and seeds usedas food.3.4 SEED STRUCTURE IN SELECTED FAMILIESSeed characteristics of 12 families of angiosperms with common crop plants aregiven. The description includes external and internal characteristics. Special featuresand variations, when present, are indicated.3.4.1 BRASSICACEAE (CRUCIFERAE) (FIGURE 3.4A TO E)(Thompson, 1933; Sulbha, 1957; Rathore and Singh, 1968; Vaughan, 1970; Vaughanand Whitehouse, 1971; Prasad, 1974)External: Seeds are small, globose, compressed or slightly flattened laterally.In the last type surface, contours usually have distinct radicle ridges and bentembryo, notched or cleft with a groove or line between the cotyledons and radicle;brown to black, yellow or white; surface is reticulate or pitted, with hilum andmicropyle inconspicuous.Internal: Seed coats two, endotestal, seed epidermis of cuboid or flattened cellswith low (Brassica nigra, B. juncea, B. rapa, and B. campestris) or high content of