154 



BOTANY AND PHARMACOGNOSY. 



ferentiated (Fig". 5yj : (i) The cotyledons; (2) the part below 

 the cotyledons, known as the hypocotvl. the apical portion of 

 which constitutes the young- root or radicle; (3) the part above 

 the cotyledons, known as the epicotyl, the apex of which con- 

 sists of a more or less developed bud spoken of as the plumule. 



\Qc 



a E 



vrr r 



Fig. 93. 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. 



The position of the embryo (Figs. 121, 122) in the seed varies 

 somewhat : in most seeds it lies in the center, as in strophanthus 

 and linuni : it may, however, be excentral. as in colchicum and 

 nutmeg. The cotyledons are usually situated above the hypocotyl, 

 but in the Cruciferae, either their edges lie against the hypocotyl, 



