REJUVENESCENCE IN NATURE. 279 



foisooation of germinal vesicles and transitory cells taking 

 place in both its ends; its primary nucleus ordinarily 

 survives,* or even increases considerably in size after 

 the formation of the germinal vesicles.f The nucleus of 

 the embryo-sac is only dissolved during or shortly before 

 the period of fertilisation, and then a profound recon- 

 struction commences in the interior of the embryo-sac, 

 expressed in the production of daughter-cells, likewise 

 free, I but so numerous that they soon exhaust the inde-, 

 pendent life of the former, and the entire cavity becomes 

 filled up by the cohering newly -formed cells. The tissue 

 produced in this way is the endosperm, or, as it is called, 

 the albumen of the seed, in which the developing embryo 

 of the new plant then becomes imbedded. The en- 

 dosperm-ceUs, like the germinal vesicles, originate as free 

 nuclei in the fluid of the embryo-sac, § which subsequently 

 become surrounded by masses of contents and clothed 

 with membranes. The cells thus formed very soon com- 

 bine into a continuous parenchyma, in which there is no 

 ■ longer evidence of the origin from free cells. || The 

 cellular fiUing-up of the embryo-sac with endosperm-cells 

 is not however completed at once, but proceeds gradually 

 from the periphery to the centre, the successively formed 

 endosperm-cells applying themselves in layers upon the 

 inside of the wall of the embryo-sac.^ The formation of 



* L. C.J Sorghum, t. xi, f. 22 ; Hyacinthus, t. siv, fig. 2 ; Erodium, t. iii, 

 f. 17 ; Helianthus, t. xiii, f. 17. More rarely the nucleus of the embryo-sac 

 vanishes before the formation of the germinal vesicles, e. g., in Orchis, t. i, 

 f. 32. 



t L. c, Agrosiemma, t. ii, f. 18 — 22 ; Bartonia, t. ii, f. 34 — 40 ; Fritillaria 

 imperialis, t. viii, f. 6 — 9. 



X The rarer case of formation of endosperm by cell-division has been men- 

 tioned previously, (p. 248.) 



§ See Hofmeister's figures of Godetia, ('Bot. Zeitung.,' 1847, t. viii, 

 f. 25, a;) Fritillaria imperial-is, ('Enstehung des Embryo,' t. viii, f. 11;) 

 Fcbalium, (1. c, t, xiii, f. 11 ;) Helianthus, (t. xiii, f. 20 ;) Linum, (t. xiv, 

 f. 4, 8.) 



II See Sohleiden, 'Beitriige zur Botanik,' t. vi, f. 69, 76, 17. (Erom the 

 albumen of Ghamadorea Sehiedeana.) (See trausl. in Taylor's ' So. Mem.,' 

 vol. ii, p. 281, t. XV, f. 1—10.— A. H.) 



% See Schleiden and Vogel, ' Ueber das Albumen,' ' Act. Nat. our.,' xix, 

 ii, t. 42, f. 42, 43 (Tetragonolobus purpureus,) and f. 49, 50 (Baptisia 



