MONOCOTYLEDONOUS GEEMINATION. 



355 



sperm or albumen ; c, the intra-seminal portion of the cotyledon, which 

 absorbs the nourishment ; p c, the petiolary or extra-seminal portion 

 of the cotyledon, which varies in length, and may be wanting ; v, the 

 sheathing portion of the cotyledon, from a slit in which, /, the plu- 

 mule, g, protrudes, supported on the axis or cauliculus, t ; while the 



Fig. 626. 



radicles, r and /, pierce the iategument at the base, and are each 

 covered with a separate sheath, m, called coleorhiza (fig. 105, p. 42). 

 In aperispermic Monocotyledons, as Alismacese and Potamese (fig. 595, 

 p. 334), the cotyledon does not remain within the seed, but is raised 

 above the ground, c, giving origin to the plumule, g, which is at first 

 enclosed in its sheath. 



Thus the cotyledon follows the development of i^eaves. Its 

 limb is first produced, and is either pushed above ground, or 

 is confined within the seed. In the latter case it is arrested iu 

 its progress ; subsequently, a sheath is formed which may either 

 be a direct continuation of the limb, or may be separated from it 

 by a petiolary portion. When the limb is confined in the seed, and 

 ceases to be developed, the sheath often continues to grow, forming a 

 marked covering of the axis. The rootlets in Monocotyledons during 

 germination (fig. 105 r r, p. 42) pierce the radicular extremity of the 

 embryo, and become covered with sheaths or coleorhizas, c c, formed 

 by a superficial layer of cellular tissue. As the radicular extremity 



Pig. 626. Germination of tlie monocotyledonous perispermic seed of Canna indica. The 

 seed is cnt to show the relation hetween the perisperm and the embryo at different stages, 

 the former diminishing, while the, latter increases, e. Envelope or spermoderm. o, Its 

 upper part, which is separated like a lid or operculum, to allow the passage of the radicle. 

 J), Perisperm or albumen, c. Cotyledon, r, Eadicle or young root. / /, Secondary 

 radicles, w, Coleorhiza or sheath of the roots. /, Slit indicating the position of the gem- 

 mule ; at this slit an elongated sheath, v, is protruded, o o. Narrow portion of the cotyle- 

 don (corresponding to the petiolary portion), intermediate between its enlarged portion, t 

 (corresponding to the lamina or limb of the leaf), and its sheathing or vaginal portion, v. 

 t, TigeUus or cauliculus. g, Gemmule or plumule. 1, First stage, in which the radicle, r, 

 begins to appear through the integuments or spermoderm. 2, Second stage, where the slit, 

 /, is seen also on the outer surface, indicating the situation of the gemmule. The true 

 radicle, r, has pierced the envelope of the seed, and at its base shows a small sheath or 

 coleorhiza. One of the small radicles, /, is also seen with a coleorhiza. 3, Third stage, 

 when all the parts are more developed, and the gemmule, g, appears on the outside of the 

 slit, /, the edges of which are prolonged in the form of a sheath or vagina, u. 



