426 Prof. H. Karsten on the Formation, 



In Cladophora glomerata, whose endogenous cells have just 

 been considered, a thickening of the originally very delicate 

 membrane of certain endogenous cells occurs regularly, but only 

 when these have acquired their normal size and by their contact 

 and pressure concur in the formation of a transverse septum 

 whilst, at the same time, the secretion-cells in their vicinity un- 

 dergo absorption. 



The more rarely occurring conditions of development described 

 in the last section seem to me also to elucidate sufficiently the 

 normal process, the essential relations of which can with diffi- 

 culty be followed in the joint-cells when completely filled with 

 chlorophyll and other secretion-materials. 



Fig. 46 shows one of the joint-cells of Cladophora poor in 

 chlorophyll and filled with the large colourless cells, such as are 

 produced by cultivation in pure distilled water, especially when 

 the plant has been cut into short pieces. The specimen has 

 been subjected for a short time to the action of dilute glycerine, 

 in order to detach the endogenous cells from the membrane of 

 the mother cell. The membranes of these cells, though sepa- 

 rated by a delicate septum, were not perceptibly thickened; by 

 the action of exosmose they were contracted and also detached 

 from each other at the septum [x), without leaving a layer of 

 deposit between them. This happens also in the case of (Edo- 

 gonium, as above described (p. 283), but appears to be of un- 

 usual occurrence. 



The conviction is thus arrived at of the actual presence of 

 free cells and of the origin of a septum by the mutual contact 

 of their walls, even before any appreciable thickening, and with- 

 out the agency of any involution or folding of the mother cell. 

 Nageli, indeed, noticed these phenomena, but nevertheless be- 

 lieved in the existence of inward-growing walls, which might be 

 invisible either on account of their tenuity or of their containing 

 a great amount of water. 



One of the two thin-walled daughter cells represented in 

 fig. 46 is seen at q to be again divided by a distinguishable 

 septum, in all respects similar to the septum displayed in (Edo- 

 gonium, as observed at its origin and represented in figs. 21-29, 

 and described at p. 277. This delicate septum would not be 

 distinguishable if the inner wall of the mother cell were, as 

 usual, coated with secretion- vesicles, until these were absorbed, 

 and the later process of thickening set up in it. In the present 

 case, the observation of this young joint-cell, which had been 

 rapidly expanded in consequence of the injury done to the 

 neighbouring cells, was rendered possible by the less degree of 

 ^aggregation of the secretion-materials. 



The cells that make their appearance on the section of a joint- 



