Development f and Structure of the Vegetable Cell. 129 



■econdary cell, with its internally adhering chlorophyll -sac, is 

 contracted upon the two daughter cells as described at p. 29 ; 

 it is finally ruptured between them in the middle, in common with 

 the chlorophylUsac, which is here likewise drawn out into a 

 thread-hke form. 



In the developmental condition shown in fig. 75, it is the 

 daughter cells, converted into new joint - cells (with their 

 endogenous cells still nearly undeveloped and of equal size), 

 that separate from their primary cell-membranes and contract 

 upon the entire solid contents, their fluid contents being at the 

 same time evacuated by exosmose. 



The septum is quite uniformly thickened, and only per- 

 forated at the point where the chlorophyll-sac is situated, — not, 

 however, in the centre of the septum, as must have been the 

 case in accordance with the notion of septum-formation by an 

 annular fold of the membrane of the mother cell constricting 

 its contents, but, in correspondence with the position of the chlo- 

 rophyll-sac before the action of the reagent, at its periphery. 



This is seen very distinctly when the septum, formed by the 

 mutual apposition of the endogenous cells, touches the chlo- 

 roph\ll-sac at the point where it contains one of the large 

 thick-walled starch-vesicles, which requires a long time for its 

 absorption. For if the septum strikes the chlorophyll-sac at a 

 thin spot between its more solid otptents, the sac is usaally 

 torn, during the action of the reagent, by the pressure exerted 

 by it upon the membrane to which it adheres, the appearance 

 being then as represented in fig. 77. 



The thickening of the primary membrane of the daughter 

 cell, which commences at the same time with the formation of 

 the septum, as also that of the secondary membrane of the 

 mother cell, advances from the septum towards the ends of the 

 mother cell ; and in consequence of this the remarkable pheno- 

 menon occurs, that the chlorophyll-sac at the ends distant from 

 the septum is covered by a membrane (figs. 75 & 77), whilst 

 near the septum (before its absorption) it lies freely upon the 

 surface of the contracting endogenous cells. 



This is probably explained by the fact that the secondary 

 membrane of the mother cell, as also the primary membrane of 

 the daughter cell, is no longer contracted by the above reagents 

 in the immediate vicinity of the septum, as they have passed 

 here from the soft and viscous into the compact and resistant 

 condition ; at some distance from the septum this contraction 

 takes place, and therefore the membranes are ruptured at the 

 limit between these two states of aggregation. 



The soft and viscous state of the cell-membranes appears to 

 me to be characteristic of the period of development which pre- 



Ann. if Mag. N. Hist. Ser. 3. V^ol. xiv. 9 



