SEED OR MATURE OVULE. 



279 



may be flattened laterally, compressed; or from above downwards, 

 depressed. They may be round, oval, triangular, polygonal, rolled up 

 like a snail, as in Physostemon ; or coiled up like a snake, as in Ophio- 

 caryon paradoxum. 



586. The great object of fertilization is the formation of the embryo 

 in the interior of the seed. In general, one embryo is produced, con- 

 stituting what is denominated monembryony (jx-dvo^ one) ; but in Coni- 

 ferse, Cycadacese, Misletoe, &c., there are frequently several embryos, 

 giving rise to what is called polyembryony (VoAwf, many). Sometimes 

 two embryos become united together in the same seed. In the coni- 

 ferous seeds, numerous corpuscles are seen whence the embryos pro- 

 ceed. The process of fertilization has already been traced until the 

 embryo appears as a rounded cellular body, enclosed in the embryo- 

 sac, and attached to a suspensor. In fig. 480, e is the embryo, and 

 a e the embryo-sac. In this sac there is at first a mucilaginous fluid, 

 the amnios, in which cells are speedily developed, commencing on its 

 inner surface, and extending towards the interior. The embryonic 

 cell (fig. 485 v), still attached to the sac by its suspensor, s, contains 

 in the early state semifluid granular matter, which becomes organized, 

 producing distinct nucleated cells (fig. 485, 2, e). These gradually 

 multiply, and form at length a cellular mass, at first undivided (fig. 

 485, 3, e), but afterwards showing a separation of parts, so that the 



axis and lateral projections or rudiments of leaves can be distinguished. 

 In figs. 486 to 491, all the stages of the formation of embryo can be 



Fig. 485.- First development of the embryo of Draba verna. o. Suspensor, which in this plant 

 is very long, v, Embryonic or germinal vesicle, e, Embryo. 1. First stage, in which the 

 embryonic vesicle only is seen. 2. Second stage, showing several cells formed in the embryonic 

 vesicle. 3. Third stage, in which the embryo becomes more conspicuous in consequence of the 

 formation of numerous small cells. 



Fig. 486. Monocotyledonous embryo of Potamogeton perfoliatus in its early stage, appearing 

 as a vesicle or simple cell. 



Fig. 487. The same farther advanced, showing radicle, >, gemmule or plumule, g, and the 

 cotyledon, c. 



Fig. 488. Dicotyledonous embryo of (Enothera crassipes in its early stage, appearing as a 

 vesicle or cell. 



Fig. 489. The same further advanced, showing three united utricles or cells. 



Fig. 490. -The same more developed, showing numerous cells. 



Fig. 491. The same in a more developed state, showing radicle, r, gemmule, </, and cotyle- 

 dons, cc. 



