DICOTYLEDONOUS EMBEYO. 337 



is alternate - with the first formed. In the Oat an abortive organ 

 called the epihlast (^XadTog, a shoot) is produced, which may be con- 

 sidered a rudimentary second cotyledon. 

 The cotyledon (fig. 600 c) is fi)lded either 5^ 



partially, as in Dioscorea, or completely. 

 Its sheathing portion (vagina) embraces the 

 bud or gemmule, which appears as a mam- 

 miUary projection ; its position being indi- 

 cated by a cleft or slit (fig. 600/, p. 336), 

 where the edges of the sheath unite. All the 

 portion of the embryo above the gemmule 

 is the cotyledon ; all bfelow, the radicle. 



Dicotyledonous Embeyo. — The form 

 of this embryo varies much ; and although 

 sometimes resembling in its general aspect 

 that of monocotyledons, yet it is always ; 

 distinguished by a division taking place at 

 the cotyledonary extremity, by which it is 

 separated, into two, more or less evident, 

 lobes. The parts of this embryo are easily 

 traced in the Bean, Pea, Acorn, and Almond. 

 In the latter (fig. 596) the embryo has an 

 oval form, consisting of two thick cotyle- 

 dons, c c, and a radicle, r. When one of 

 the cotyledons is removed (fig. 597), leaving 

 scars, ic, the gemmule or plumule, g, is 

 seen included between them, with its cauli- 

 cule or tigelle, t. 



The cotyledons are not always, however, 

 of the same size. Thus, in a species of 

 Hirsea (fig. 602), one of them, c', is smaller 

 than the other; and in Carapa guianensis 

 (fig. 603) there appears to be only one, in 

 consequence of the intimate union which 

 takes place between the two, as indicated by 

 the dotted line, c. The union between the 

 cotyledonary leaves may continue after the 

 young plant begins to germinate. Such em- 

 bryos have been called psmio-monocotyle- 

 donous (-^/ivdrjg, false). When there are 

 two cotyledons, they are opposite to each 

 other. In some cases there are more than two present, and then 



_— / 



Kg. 601. S i 



Fig. 601. MonoGotyledonouB embryo of Zannichellia palustris germinating, m, Collum 

 or neck, the point intermediate between the stem or tigelle, t, and the radicle or root, r. 

 c. Cotyledon, g, Gemmule or plumule. ; 



Z 



