336 MONOCOTYLEDONOUS EMBRYO. 



Cuscuta (fig. 598) the embryo appears as an elongated axis without 

 divisions ; and in Caryocar butyrosum (fig. 599) the mass of the embryo 

 is made up by the radicular extremity and tigelle, t, in a groove of 

 which, s, the cotyledonary extremity lies embedded, which when 

 separated, as in the figure, shows only very small cotyledons. In 

 some monocotyledonous embryos, as in Orchidaceee, it requires a micro- 

 scopic examination to detect the cotyledonary leaf. 



Monocotyledonous Embryo. — In this embryo the single coty- 

 ledon in general encloses the gemmule at its lower portion, and 

 exhibits on one side a small slit (fig. 600 /), which indicates the edges 

 of the vaginal or sheathing portion of the cotyledonary 

 leaf. The embryo presents commonly a cylindrical form, 

 rounded at the extremities, or a more or less elongated 

 ovoid (fig. 600). At first sight there seems to be no dis- 

 tinction of parts ; but on careful examination, by moisten- 

 ing the embryo, and making a vertical section, there wUl be 

 detected, at a variable height, a small projecting mammilla, 

 buried a little below the surface. This is the gemmule 

 which marks the termination of the axis. From the lower 

 extremity proceeds the radicular portion (figs. 595 t r, 

 "■ 600 r), which may be said to represent both the tigelle 



^' ■ and radicle. The upper portion or chalazal end of the 

 embryo is the cotyledon (figs. 695, 600 c), which is sheathing at its 

 base, so as to enclose the gemmule. In some cases, as in the com- 

 mon oat [Avena sativa), there is a peculiar process which covers the 

 plumille, and which is considered by some as an axillary stipule of 

 the cotyledon. The length of the radicular portion, or that below 

 the gemmule, varies. It is usually shorter than the cotyledon, 

 and is denser in structure ; but in some instances it becomes much 

 larger, giving rise to what has been called a macropodous embryo (/laxgog, 

 long, and 'nroug, a foot). Thus, in fig. 601, t represents the long radi- 

 cular portion in the young state, whence ultimately the root, r, 

 proceeds. Occasionally, the radicular portion becomes very thick and 

 large, so as to form a considerable portion of the embryo ; and in all 

 monocotyledons it may be considered as an enlarged mammHlary 

 projection, whence the rootlets (adventitious roots) proceed , by 

 bursting through it, and carrying with them a covering or sheath, 

 coleorhiza (fig. 105, p. 42). 



When considering endogenous or monocotyledonous stems, it was 

 shown that the leaves are produced singly and alternately, in a 

 sheathing manner, each embracing the subsequently developed bud. 

 So it is in the monocotyledonous embryo. There is a single leaf or 

 cotyledon produced, and if in any instance there is more than one, it 



Kg. 600. Embryo of TriglooUn Barrelieri. r, Badicle. /, Slit corresponding to the 

 gemmnle. c, Cotyledon. 



