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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, epidermis; 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, aleurone, and other food materials, like the cells of the 



