Development, and Structure of the Vegetable Cell. 277 
the lower sheath-like portion of the circularly torn membranous 
wall, in consequence of the gradual expansion of the inferior 
mass of the cell-contents. Bary regards the lower of the two 
new and simultaneously produced cells as the parent of the 
upper. 
The real process of cell-multiplication does not agree with 
this description. The transverse cell-wall does not originate 
only outside the enveloping membranous sheath, in accordance 
with the prevailing opinion, by the inward growth, from the 
surrounding wall of the elongated mother cell, of a fold-like or 
lamelliform horizontal septum ultimately meeting at the centre, 
but, on the contrary, it is present and complete before the rup- 
ture of the membranous wall and the occurrence of the abrupt 
elongation of the mother cell. 
The thickening, and not the formation of the transverse sep- 
tum, follows after the changes described by Bary have taken 
place in the mother cell when this escapes from the membranous 
enveloping sheath, which until then encloses that portion of the 
joint-cell in which the transverse septum arises, by the develop- 
ment of daughter cells, in precisely the same way as the forma- 
tion of cork-cells in Philodendron pertusum has already been 
described. . 
The existence of the transverse septum in the joint-cells which 
are not yet elongated, and indeed in those in the upper end of 
which the fold of the mother cell is already produced, is parti- 
cularly easy of demonstration in the species of the genus Cdo- 
gonium, as Hartig and others have indeed actually witnessed ; 
but it is not so with respect to the mode of origin of the septum. 
The great quantity of chlorophyll- and starch-corpuscles which 
cover the inner surface of the cell-walls of these plants, when in 
vigorous growth, renders it impossible to make out with any 
certainty the development of new cells within these joint-cells. 
In my researches I employed plants of Cidoyonium grande 
which had been raised from spores in pure water, and many of 
whose cells were scantily occupied by chlorophyll, so that the 
changes which took place in the other contents could be more 
clearly examined. 
In such plants it is possible to make out the true mode of 
formation of the septum, which is thus effected :—two of the 
many non-nucleated hyaline cells which occupy the interior of 
the joint-cell acquire a greater size (Pl. V. figs. 21, 26, & 28), 
and by their growth press the others to one side against the 
wall of the mother cell (which is coated with chlorophyll, starch, 
&c.), and eventually come into contact and by their mutual ap- 
position form the septum, often obliquely placed at first, and 
completely fill up the cavity of the mother cell (figs. 27 & 29), 
