278 Prof. H. Karsten on the Formation, 
This process occupies some few minutes ; and in order to observe 
it the eye must be fixed upon some one such cell containing but 
little chlorophyll, and in which the fold of the wall is fully 
formed, though a septum be as yet not present in it. 
After the septum has attained the characters of a complete 
disk dividing the cell-cavity, an act of growth, or at least an 
expansion of the cell-wall, still goes on, whereby the rather 
obliquely placed septum acquires a horizontal direction, and a 
certain amount of pressure is at the same time exerted upon the 
cell-wall, which forces apart or extends the fold (above which 
the enveloping membrane is torn through), and thus enlarges 
by about one-third of its length the mother cell of the two 
newly developed cells (figs. 22 & 23). 
Contemporaneously with this sudden evolution of the mother 
eell, the two endogenous cells undergo expansion. When both 
these cells are not equally enlarged, it is, as a rule, the upper 
one (usually the smaller of the two) which at first expands compa- 
ratively more strongly, and at the same time downwards towards 
the new septum, whilst the chlorophyll- and starch-vesicles, com- 
pressed against the walls of the mother cell, do not at first 
undergo very much displacement. This is the reason why, 
at the first moment after the extension of the mother cell, the 
new septum is usually found free from secretory vesicles, and 
only bounded by a transparent watery fluid (Bary’s colourless 
layer), as happens also with the inferior extremity of the lower 
of the two daughter cells. 
This primary and abruptly accomplished enlargement of the 
endogenous cells, after the laceration of the enveloping mem- 
brane, is, like that of the mother cell itself, only a mechanical 
act,—not a process of growth, but merely the extension of the 
cell-wall already enlarged by assimilation. The secretion-cor- 
puscles, however, gradually distribute themselves equally over 
the whole surface—except that, quite at the upper end, at the 
summit of the mother cell, a compact group of these secretion- 
corpuscles remains, even in cells otherwise almost destitute of 
such contents, whilst the lower extremities of the two young 
daughter cells usually continue longest free from these sub- 
stances, and appear colourless. 
Nevertheless, this distribution of the secretion-material is not 
so rigorously subjected to the rule just mentioned. as not to 
admit of exceptions. 
These relations are, however, it appears to me, worthy of 
notice, because they may furnish data for arriving at conclusions 
respecting the place of formation of the secretory material, the 
direction of the cell-growth, and therefore the direction or course 
of the nutritive matters distributed in the series of cells. 
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