Development, and Structure of the Vegetable Cell. 129 
secondary 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 chlorophyll-sac, which is here likewise drawn out into a 
thread-like 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 
ease 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- 
rophyll-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 contents, the sac is usually 
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. & Mag. N, Hist. Ser. 3. Vol. xiv. 
