THE HIGHER CRYPTOGAMIA. 407 



takes place in length, breadth, and thickness. With the 

 commencement of the cold season the walls of the endo- 

 sperm which fills the embryo-sac become much thick- 

 ened, and exhibit lamination of the gelatinous substance of 

 the thickened portions (PL LIX, fig. 13). If delicate 

 sections of the endosperm are placed in water, the gela- 

 tinous matter of the thickening layers of the cell-walls 

 becomes rapidly and easily dispersed in the fluid ; the pri- 

 mordial utricles of the cells then lie free in the cell-cavity 

 (PI. LIX, fig. 17). The thickened walls of the central 

 cells of the endosperm are the most sensitive to the action 

 of water. This peculiar nature of the cells of the transitory 

 endosperm of the first year renders the observation of their 

 walls especially difficult.* 



At the beginning of March the dissolution of the 

 thickened cell-walls of the endosperm commences. Each 

 of the primordial cells thus made free exhibits a large 

 central spherical nucleus filled with brighter fluid (PI. LX, 

 fig. 1). About April this nucleus is dissolved; cells 

 whose nuclei have been just absorbed contain 'numerous 

 spherical drops of a highly refractive substance, which 

 nearly fill the cell. Further developed cells contain two 

 (PI. LX, fig. 1*), others four, many only three nuclei. 

 Around each such nucleus a free daughter-cell is formed, 

 originally of a spherical shape, lying free in the mother-cell. 

 By absorption of the wall of the mother-cell the daughter- 

 cells become free ; the same process is repeated in their 

 interior (PL LX, fig. 3). Thus the number of the cells 

 enclosed by the embryo sac increases very rapidly in geome- 

 trical progression. The embryo-sac itself grows in a re- 

 markable manner to more than twenty times its previous 

 volume by pushing aside the loosened cells of the adjoining 

 portions of the nucleus of the ovule ; its wall, hitherto very 

 tender, becomes thick and glassy, and ultimately granulated 

 on the outer surface. At the same time a very active mul- 



* The earlier observers considered the embryo-sac filled with cellular tissue 

 to be a cavity in the tissue of the nucleus (Hartig, < Naturgeschichte der Forst- 

 culturpflauzen,' see the explanation to fig. 17 of Plate xxv. Gottsche, JJot. 

 Zeit.,' 1845, p. 380). Quite lately Pineau pointed out its true nature (' Ann. d. 

 Sc. Nat.,' iii ser. vol. ii, p. 85). 



