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A TEXT-BOOK OF BOTANY. 



all of the ovules of the pistil fertilized, hence the number of seeds 

 is usually less than the number of ovules. 



Structure of Seed. — After the fertilization of the egg-cell 

 certain changes take place in the embryo-sac: At one end the 

 developing embryo is attached to the wall by a short stalk or 

 suspensor (Fig. 82) ; the nuclei, lying in a mass of cytoplasm 



Fig. 248. Citrullus Colocynthis. A, seed: a, in longitudinal section, and b, surface view; 

 S, deep clefts or fissures; m, micropyle; g, hilum; w, radicle; c, cotyledons. B, parenchyma 

 cells of ripe fruit showing simple pores, the walls are colored blue with chlor-zinc-iodide. 

 C, longitudinal section of wall of pericarp of ripe fruit showing e, epidennis; p, parenchyma; 

 Sc, sclerotic cells which gradually pass into a thick-walled parenchyma consisting of small 

 cells (p'); g. spiral vessels; P, isodiametric, porous parenchyma cells, containing air and of 

 which the fruit for the most part consists. D, cross-section of seed-coat showing, G, an 

 outer layer which is more or less easily separable from the rest of the seed and the walls of 

 which are somewhat mucilaginous; E, epidermis of palisade-like cells; Sc, sclerotic cells; PI, 

 a layer of tabular cells with undulate walls; T, a layer of small somewhat branching cells, 

 the walls of which are not strongly thickened and either porous or reticulate; P, several 

 layers of parenchyma and the collapsed epidermis; Pe, perisperm; En, endosperm. E, 

 tangential section of tabular sclerotic cells of seed-coat shown in PI in Fig. D. — After Meyer. 



around the wall of the embryo-sac, divide and re-divide ; the large 

 vacuole in the center becomes filled with a watery or milky fluid, 

 and later the nuclei, with portions of the cytoplasm, may be 

 enclosed by a cellulose wall and become permanent cells, in which 

 the embryo is embedded. Likewise in the nucellus, changes are 

 also taking place ; the cells are found to be dividing, and storing 

 starch, oil, akurone, and other food materials, like the cells of the 



