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 

 sabstance, as represeuted in fig. 32. 



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 PI. VI. fig. 42 a, where the contents are 

 distinctly divided into three segments, each enclosed by a deli- 

 cate 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, pi. 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 



