SEED OB MATURE OVULE. 



331 



rise to what is called ■polyemhryony {vo'khg, many). Sometimes two 

 embryo^ become united together in the same seed. In the coniferous 

 seeds numerous corpuscles are seen, whence the embryos proceed. The 

 process of fertilisation 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. 576, e is the embryo, and se the embryo-sac. 

 In this sac there is at first a protoplasm, in which cells are developed. 

 The embryonic cell (fig. 581 v), still attached to the sac by its suspensor, 

 s, contains distinct nucleated cells (fig. 581, 2 e). These gradually 

 multiply, and form at length a cellular mass, at first undivided 

 (fig. 581, 3 e), but afterwards showing a separation of parts, so that the 

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



582. 



684. 



Fig. 681. 



Fig. 683. Fig. 686. 



Fig. 587. 



In figs. 582 to 587 all the stages of the formation of embryo can be 

 traced; appearing first as a simple cell (figs. 582, 584), forming others 

 in its interior (figs. 585, 586) ; and finally, the parts of the embryo 

 becoming visible, figs. 583, 587, where g r \s the axis representing the 

 stem and roots, and e'e are the lateral projections, which are developed 

 as leaf-like bodies, called cotyledons (KorSXtiSiiv, the name of a plant 

 having leaves like seed-lobes). 



Peeispeem oe Albumen. — As the embryo increases in size it 

 gradually causes absorption of the cellular tissue in the embryo-sac, and 

 it is sometimes developed to such a degree as to reduce the nucleus and 

 embryo-sac to a thin integument. In such a case the seed consists of 



Fig. 581. First development of the embryo of Draba verna. o, Suspensor, wbicli in this 

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

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

 embryonic vesicle. 8, Third stage, in which the embryo becomes more conspicuous in 

 consequence of the formation of numerous small cells. Fig. 582. Monoootyledonous 



embryo of Potamogeton perfoliatus in its early stage, appearing as a vesicle or simple ceU. 

 Pig. 583. The same, further advanced, showing radicle, r, gemmule or plumule, g, and the 

 cotyledon, c. Fig. 584. Dicotyledonous embryo of (Enothera crassipes in its early stage, 

 appearing as a vesicle or cell. Fig. 585. The same, further advanced, showing three 

 united utricles or cells. Fig. 686. The same, more developed, showing numerous cells. 

 Fig. 687. The same in a more developed state, showing radicle, r, gemmule, g, and cotyle- 

 dons, cc. 



