— 166 — 



The length of the bristles differs very much and it is impos- 

 sible to say anything in general about it even with respect to a 

 single species. Sometimes the length of the bristles is several times 

 that of the alga but sometimes it is much smaller and the length 

 of the bristles in a single tuft may also differ very much. 



In the same manner the number of the bristles differs very 

 much in a single species. Even for a single specimen it is very 

 difficult, if not impossible, to give a definite number, owing to the 

 just mentioned cleaving together, that always takes place in a 

 greater or smaller degree. 



The bristles were always, where I have been able to make a 

 close investigation, gathered in tufts. These project partly from 

 the cell processes, partly from the angles of the cell junctions, 

 partly more casually from the cell surface. But this will be treated 

 more fully under the description of the species. Moreover I have 

 always noticed that the tufts are issuing from a little knob of a 



Meyen. The cell was dead and its contents had Solved in eaU de Javelle, the 



same is no doubt the case with Scenedesmus acutus and Sc. acu- 

 minatus, but as yet I have not been able to establish it with cer- 

 tainty. 



As partly pointed out by Zacharias (1903) bristles are not 

 found in all specimens of the same species, not even in one and 

 the same plankton sample and sometimes they are found on some 

 cells in a coenobium and not on others. 



But with respect to this I shall remark that it is very likely 

 that these delicate organs on a great many of the specimens may 

 be removed in a totally mechanical way during the preparation. 

 Moreover I believe to have observed that they are neither found 



Fig. 1. Pediastrum duplex Meyen var. clathratum 



A. Br. Treated with eau de Javelle (X 730). 

 Fig. 2. The apex of a cell of Pediastrum simplex 



Fig. 1. 



more refractive substance than 

 the cell wall and deeper stained 

 in the colouring preparations. 

 (Figs. 3, 4, 7, 11). [Zacharias 

 1899: Die knöpfchenartige Ver- 

 dickung]. At the Pediastrum 

 species this little „knob" on the 

 cell processes appeared to be 

 situated in a little deepening 

 and when the knob was dis- 



decayed so that only the cell-walls were left 

 (X 730). 



cell wall of the deepening ap- 

 peared distinctly (Figs. 1, 2). The 



