DICOTYLEDONOUS GERMINATION. 



301 



r and r', pierce the integument at the base, and are each covered with 

 a separate sheath, c o, called coleorhiza (fig. 124). In aperispermic 

 Monocotyledons, as Alismacea? and Potameae (fig. 505), the cotyledon 

 does not remain within the seed, but is raised above the ground, c, 

 giving origin to the plumule, <7, which is at first enclosed in its sheath. 



628. Thus the cotyledon follows the development of leaves. Its 

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

 fined within the seed. In the latter case it is arrested in its progress; 

 subsequently, a sheath is formed which may either be a direct con- 

 tinuation 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 roots in Monocotyledons during germina- 

 tion (fig. 124 r r), pierce the radicular extremity of the embryo, and 

 become covered with sheaths or coleorhizas, c c, formed by a super- 

 ficial layer of cellular tissue. As the radicular extremity thus remains 

 within the embryo, and sends out radicles from its surface, the plants are 

 said to be endorhizal (sv^oy, within, and /$/, a root). See ^[ 127. 



629. Dicotyledonous Germination. In Dicotyledons, the cotyledons 

 generally separate from the integuments, and either appear above 

 ground in the form of temporary leaves (figs. 528, 529 c c), which differ 

 in form from the permanent leaves of the plant (fig. 529 g\ or remain 

 below as fleshy lobes. In the former case they are epigeal (tiri, upon or 

 above, and ye, the earth); in the latter case (as in Beans, Arachis, 

 &c.), they are hypogeal (tiro, under). The cotyledons usually separate, 

 but sometimes they are united, and appear as one. In all cases, the 



Fig. 527. Germination of the monocotyledonous perispermic seed of Canna indica. The seed 

 is cut to show the relation between the perisperm and the embryo at different stages, the for- 

 mer 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, p, Perisperm or 

 albumen, c, Cotyledon, r. Radicle or young root, r 1 r 1 , Secondary radicles, c p, Coleorhiza or 

 sheath of the roots. /, Slit indicating the position of the gemmulc; at this slit an elongated 

 sheath, r, is protrude! p c, Narrow portion of the cotyledon (corresponding to the petiolary 

 portion), intermediate between its enlarged portion, c (corresponding to the lamina or limb of 

 the leaf), and its sheathing or vaginal portion, r. t, Tigellns or cauliculus. g, Gemmule or 

 plumule. 1. First stage, in which the radicle, r, begins to appear throilgh 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, r 1 is also seen with a coleo- 

 rhiza. 3. Third stage, when all the parts are more developed, and the gemmule, <7, appears on 

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



