Development, and Structure of the Vegetable Cell. 127 
belong exclusively to the cell-nuclei as above described, but that 
the two large secretion-cells (figs. 61 and 72) may constitute the 
foundation of the new joint-cells; in many species these show 
their relationship to the tissue-cells by their enclosing two large 
and often many smaller cells. 
These two secretion-cells, which gradually become so much 
enlarged that at length they fill the whole cavity of the joint- 
cell (the other equivalent cells diminishing at the same time), 
consequently represent the two colourless, rapidly enlarging 
daughter cells, which become developed into new joint-cells, 
and which, in Gidogonium, may be recognized as being of this 
nature by direct observation throughout all their stages of 
development. 
This, however, has not hitherto been possible in the case of 
the very fragile Spirogyra, and hence we are compelled to com- 
bine many observations of details in order to obtain a connected 
picture of their mode of development; and in this errors are 
all the more likely to creep in, as the investigation of the de- 
velopment of the colourless cells in the interior of the joint-cells 
must be assisted by reagents, the mode of action of which is 
not yet satisfactorily ascertained. 
Let us first consider those species in the elongated joints of 
which cell-nuclei are present, but do not appear to produce any 
daughter cells. If this be really the case, the new joint-cells in 
these species would be normally formed within the secondary 
cell of the joint-cell. 
Fig. 74 represents a joint-cell of S. Weberi, which is divided 
into two halves by the newly formed, delicate, and still flat 
septum, whilst the chlorophyll-sac, completely coherent, is still 
closely applied to the inner surface of the mother cell, as has 
already been described in S. princeps. If this condition be 
observed for a few hours, we may see distinctly how the sub- 
stance of the chlorophyll-sac, at its point of contact with the 
septum, loses its green colour, and finally becomes completely 
absorbed ; in from four to five hours this process has advanced 
to the condition represented in fig. 76, in which the chlorophyll- 
sac is divided into two perfectly separate portions. At this 
time the septum does not yet exhibit any indication of the 
annular fold which is subsequently formed. 
No doubt, during this absorption of the secretion-material 
of the mother cell, corresponding new formations take place in 
the daughter cells, but these cannot be observed here as in 
Cdogonium. 
A phenomenon which is probably repeated in most young 
tissue-cells is, that the organized secretion-materials, and espe- 
cially the starch and chlorophyll, adhere during their growth to 
