284 MONOCOTYLEDONOTJS EMBRYO. 



dons, the other having been removed and leaving a cicatrix, i c ; while 

 in fig. 499, the gemmule, ^, of Potamogeton perfoliatus, is covered by 

 the single cotyledon, c. 



594. The gemmule as well as the cotyledon are sometimes obscurely 

 seen. Thus, in Cuscuta (fig. 502), the embryo appears as an elon- 

 gated axis without divisions ; and in Pekea 

 butyrosa (fig. 503), the mass of the em- 

 bryo is made up by the radicular extremity 

 and tigelle, , in a grove of which, s, the 

 cotyledonary extremity lies embedded, which 

 when separated, as in the figure, shows only 

 very small cotyledons. In some monocotyle- 

 donous embryos, as Orchidaceae, it requires 

 a microscopic examination to detect the 



cotyledonary leaf. 



595. irionocotyledonous Embryo* In this embryo, the single cotyle- 

 don in general encloses the gemmule at its lower portion, and exhibits 

 on one side a small slit (fig. 504/), 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. 504). At 

 first sight there seems to be no distinction of parts ; but on 

 careful examination, by moistening the embryo, and making 

 a vertical section, there will 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. 

 499 t r, 504 r), which may be said to represent both the tigelle 

 and radicle. The upper portion or chalazal end of the em- 

 bryo, is the cotyledon (figs. 499, 504 c), which is sheathing at 

 its base, so as to enclose the gemmule. 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 macra- 

 podous embryo (potx.^;, long, and vwc., a foot). Thus, in fig. 505, 

 t represents the long radicular 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 



Fig. 502. Spiral embryo of Cuscuta or Dodder. 



Fig. 503. Embryo of Pekea, butyrosa. t. Thick tigelle or caulicule, forming nearly the whole 

 mass, becoming narrowed and curved at its extremity, and applied to the groove", s. In the 

 figure this narrowed portion is slightly separated from the groove, c, Two rudimentary 

 cotyledons. 



Fig. 504. Embryo of Triglochin Barrelieri. r. Radicle. /, Slit corresponding to the gemmule. 

 e. Cotyledon. 



