Development, and Structure of the Vegetable Cell, 429 
lamina of deposit (thickening layer), advances into the cavity of 
the cell and unites at its centre. 
Between the secondary cell and the chlorophyll-layer a colour- 
less mucous fluid collects during this process. This fluid is held 
by Dippel (Vegetabilische Zellenbildung, 1858, p. 32) to be 
plasma, which originates in this situation on account of the 
active generation of tissue going on in it, and which forces the 
green contents towards the interior as a consequence of its ac- 
cumulation. Not unfrequently, when this plasma is first seen, 
there is no perceptible trace of the septum, which subsequently 
makes its appearance, commencing from the periphery in such a 
manner that, as it has been described, it seems to be a product 
of crystallization. But that the delicate walls of the daughter 
cells may be here actually present, though hidden in the mucoid 
plasma, the previously recorded action of solution of tannin upon 
the mucous contents of the cells of Mougeotia afford sufficient 
evidence. 
Concurrently with the first indications of the presence of a 
septum (at times, indeed, previously), the mass of chlorophyll re- 
cedes towards the middle line of the cell : it seems as if the green 
contents were separated all round by the colourless plasma and 
on each side by the narrow lamina from the neighbouring walls 
of the joint-cell, and pressed towards the middle line of the 
latter,—not divided, but for the present constricted (fig. 40). 
_ In this case, however, the constriction or compression of the 
chlorophyll-mass is only apparent; for a closer examination of 
this condition shows that the vesicles which form the chlorophyll- 
layer do not actually withdraw, but have become colourless in 
the spot occupied by them, whilst the adjoining septum makes 
its appearance more distinctly. Sometimes a green vesicle re- 
mains somewhat longer in the colourless mass, and may be 
distinctly seen to grow progressively more and more colourless, 
The mode of deposition of the elongated starch- and chloro- 
phyll-vesicles in the so-called constriction (fig. 40 a) often gives 
rise to an appearance as if these corpuscles were deposited on 
the wall of a tube, continually constricted at that part, and 
particularly so in the last stages of thickening of the septum, 
where they stand at right angles to it; nevertheless it may be 
observed, especially in wide cells, that here also at their centre 
there exists a lighter cavity elongated in the direction of the 
septum which is undergoing alteration,—a cylindrical body, a 
cell which exerts its influence upon the deposition of the chloro- 
phyll during absorption. 
However, this arrangement of the secretion-vesicles is liable 
to very great variation: the condition represented in fig. 40 a, 
and previously described, is very often met with; frequently, in, 
