422 Prof. H. Karsten on the Formation, 
subsequently divided into joints (sections) by the formation of 
endogenous cells. 
The first indication of young joint-cells in the root-cells, both 
in their extreme points immediately within the enveloping mem- 
brane (fig. 32) and in the interior of the joint-cells already pre- 
sent, consists in the appearance of a continually enlarging cell, 
which at first shimmers through the chlorophyll, but afterwards 
becomes free in its median part by the displacement of the 
chlorophyll, and exhibits in its interior small vesicles, the 
rudiments of new cells. I have not completely traced in one 
and the same root-cell the entire absorption of the chlorophyll, 
starch, &c. which at first separate the daughter cells of the 
second order; but I have seen, in different individuals, «all the 
transition-forms up to states in ‘which there were no longer any 
organized bodies between the two new joint-cells of the root-cell, 
but only an apparently gelatinous, unorganized, intercellular 
substance, as represented in fig. 382. 
The membrane of the endogenous cells of the root-cell always 
appears to be thicker at the lower than at the upper end; there-— 
fore where two cells are in immediate contact, the portion of the 
lower cell entering into the structure of the septum is easily 
overlooked, especially as it is here not only a very thin mem- 
brane, but also somewhat thrust backward by the convex ex- 
tremity of the contiguous thickened cell. 
At the extremities of the stem and of the branches the oppo- 
site conditions are met with. We indeed equally find at times 
the contents of the last joint-cells composed of several thin- 
walled cells, as seen in Pl. VI. fig. 42 a, where the contents are 
distinctly divided into three segments, each enclosed by a deli- 
eate membrane. The upper extremity of the lowest cell here 
projects somewhat within the lower and concave end of that 
next above it; consequently the septa of these young cells (dis- 
coverable with the greatest difficulty) are not flat, but conical. 
The uppermost little cell discernible at the summit of a branch — 
is filled with vesicles as yet scarcely coloured green. Similar 
vesicles are found at the extreme ends of root-cells: this serves — 
to contradict the erroneous supposition that this Alga has no 
terminal growth. I have also observed a similar phenomenon 
in Vaucheria (op. cit. p. 90, pl. 2. fig. 2). 
The apex of the root-cell, which is usually thinner (fig. 42) 
and ramified at its extreme end, where it is adherent to other 
bodies, generally of organic nature (figs. 43 & 44), shows a very 
remarkable independence in the growth of its outermost cell- — 
membrane, which encloses the whole root just as the cuticle 
does the up-growing stem. This cell-membrane, independently — 
of that of the enclosed cells, emits branches which become much ~ 
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