FORMATION OF THE EMBRYO. 317 



membrane, makes no further growth, and after a time begins to 

 * wither away. It may here be remarked that the pollen-tube with- 

 ers or decays from above downwards; when its course is long, 

 the end in connection, with the pollen-grain commonly withers 

 while the other end is still growing onwards towards the ovule. 

 Within the embryo-sac near or at its apex (or micropylar end), 

 and, in some cases at least, before the pollen-tube enters the ovule, 

 a small cell makes its appearance ; this is the embryonal vesicle or 

 germinal vesicle. This cell is either developed in contact with the 

 membrane of the embryo-sac, or it soon adheres to it by one end, 

 very near but not always exactly opposite the point to which the 

 apex of the pollen-tube is applied without. This cell is the proper 

 germ or rudiment of the embryo. It is fertilized, apparently, by 

 the imbibition of the fluid of the pollen by endosmosis through the 

 intervening membranes, namely, that of the pollen-tube, that of 

 the embryo-sac, and that of the embryonal vesicle itself; the vital- 

 ly active contents of two cells of different origin being thus com- 

 mingled, as in the simpler process of conjugation in the lower Cryp- 

 togamous plants (102). Thus endued with new force, the embry- 

 onal vesicle, which would otherwise soon wither away, at once 

 commences an active development ; it elongates downwards, or 

 from its free extremity ; minute granular matter appears in the 

 interior, which was before perfectly clear and transparent ; soon a 

 few transverse partitions are seen, and it is thus converted into a 

 chain of cells, each of which contains a distinct nucleus. This 

 body, which may attain considerable elongation, by the continued 

 elongating growth and division of the terminal cell (32-34), be- 

 comes the Suspensor. The lowest of its cells retains a globular 

 shape, and enlarges ; its contents become turbid, and are converted 

 into a mass of delicate cells, either by original cell-formation in 

 the interior (28), or by cell-division (31, if there be indeed any 

 real difference in the two modes), as before, only that here the di- 

 vision takes place in every direction. This globular body, hung 

 on the extremity of the suspensor, is the Embryo (Fig. 430). 

 As it grows it soon begins to assume its proper form. In a 

 Dicotyledonous plant, as is rudely shown in the annexed figures, 

 the end farthest from the suspensor begins to be two-lobed (Fig. 

 432) ; the lobes increase by ordinary cellular growth, and form 

 the Cotyledons (Fig. 433, 434) ; the opposite extremity is of 

 course the Radicle. The suspensor usually disappears before the 

 27* 



