Development, and Structure of the Vegetable Cell. 35 
side of the original cell-nucleus, arranged in correspondence 
with the transverse diameter of the joint-cell. In the next 
stages of development they take up a position in accordance 
with the longitudinal axis of the cell within the nuclear cell, 
which has now become globular. A glance at figs. 81 & 83-85 
will render this condition quite clear. These are nuclear cells 
of Spirogyra nitida, Kg., such as often occur in cultivated ex- 
amples of this species, with their membranes distended by the 
action of water containing carbonic acid. 
Fig. 84 shows very distinctly that the new cell-nuclei, which 
here contain no nucleoli, are enveloped by the outer membrane 
of the cell-system produced by the development of the cell- 
nucleus. 
In fig. 85 these two new cells (the daughter cells of the entire 
cell-system) are still more expanded within their mother cell, so 
that they surround the nuclear cell lying between them, and 
enclose it with their contiguous membranes (as also in fig. 81). 
The nuclear cell, however, still exists uninjured between 
them, as in fig. 84 (and fig. 83 shows another similar state of 
development seen from the side), although its absorption now 
generally begins, and at the same time a secondary cell is _pro- 
duced in each of the daughter cells. The daughter cells, dis- 
tended by carbonic-acid water, here represented contain as yet 
no cellular structures, such as are ordinarily present in norm- 
ally developed cells at this stage of development. 
In fig. 81 a normal case is represented; a cell-nucleus is 
situated in the daughter cell on the wall directed towards the 
centre of the new joint-cell, as is the rule in Spirogyra, and 
therefore on the side opposite to the original cell-nucleus. 
This cell-nucleus of the young daughter cell usually appears, 
in its earliest grades of development, in the form of a spherical 
accumulation of mucilage. In this mucilage, however, in other 
cases, a vesicle may be seen imbedded, and, a little later, one or 
rarely several nucleoli may be detected. 
That the external membrane of the cell-nucleus (which, as 
already stated, is frequently seen, in some Spirogyre, to be com- 
posed of several endogenous cells, and therefore developed into 
a complete cell-system) may attain, just as in Gidogonium, to 
the full size of the mother cell is shown by states such as that 
represented in fig. 80, which are met with occasionally, although 
rarely, in cultivated plants of Spirogyra. (Fig. 80 is drawn 
from a specimen which had lain for some time in carbonic-acid 
water ; and this certainly assisted somewhat in the distention of 
the cell-membrane, as it also caused the primary membrane of 
the joint-cell to become particularly prominent.) 
Not unfrequently, in a disproportionately long cell, two cell- 
Ann. & Mag. N. Hist, Ser.3. Vol. xiv. 3 
