428 Prof. H. Karsten on the Formation, 



before one of the two cells has extended itself more or less com- 

 pletely from the cylindrical cavity of the mother cell in the form 

 of a branch. It might be imagined that it is so forced out by 

 the contemporaneous predominant growth of the sister cell. 

 This regular course of branch-formation is not, however, always 

 thoroughly carried out ; the lower extremity of the branch-cell 

 frequently remains within the mother cell, and aids to form 

 along with its sister cell a septum in the form of an oblique or 

 horizontal thickened lamina. 



The externally visible phenomena which accompany the pro- 

 cesses of normal septum-formation in C. glomerata may readily 

 mislead one into regarding the explanation given of them by 

 Mohl as the natural one. 



Having, however, ascertained that in the joint-cells of C. glome- 

 rata there is generally concealed beneath the superficial layer of 

 secretion -cells a complete tissue of endogenous cell-systems — a 

 tissue which certainly does not cohere, like the cellular tissue of 

 more highly organized plants, by intercellular substance, or at 

 least not by such as is insoluble in water and which consists, 

 not of persistent tissue-cells, but almost entirely of transitory 

 secretion-cells (for large mother cells may be seen, filled with cells 

 of nearly half the size of a joint-cell, to swell forth from the cut 

 joint of the Conferva), — having ascertained that the flat horizontal 

 septum produced by the mutual apposition of these endogenous 

 cells occurs already formed (fig. 46 q) in the secondary cell be- 

 fore this has become thickened, and having been able in certain 

 cases, by means of endosmotic fluids, to divide this septum and 

 to recognize its composition out of parts of two neighbouring 

 cells (fig. ^iQx), — having, further, even in C. glomerata, excep- 

 tionally seen septa normally formed by the mutual apposition 

 of two cells originally separate (p. 419, fig. 32) and even belong- 

 ing to diff'erent generations, — we shall feel called upon to submit 

 the normal process of septum-formation in this plant to another 

 examination in order to try to refer it to the general law of cell- 

 formation. 



Fig. 40 a (PL VI.) exhibits the phenomenon first witnessed 

 by Dumortier (Nova Act. Leop. -Carol. 1832) and described in 

 detail by Mohl, which is regarded by him and his followers as a 

 folding of the walls of the joint-cells of C. glomerata in process 

 of multiplication, and as the type of " cell-formation by fission.^^ 



Mohl (Vermischte Schriften, 1845, p. 623; Veget. Zell. 1851, 

 p. 212; Botanische Zeitung, 1855, p. 689) supposed that the in- 

 ternal surface of the secondary cell (primordial layer) is overlaid 

 with a granular mucoid protoplasm, the chlorophyll-layer, which 

 gives way at the same time or nearly so that the involution (fold) 

 of the walls, formed by the primordial layer and the youngest 



