— 172 — 



species is much rarer than the preceding one. I have only found 

 some specimens of it in a single pond. These did have bristles, 

 but I was not able to see their arrangement distinctly. 



Pediastrum simplex, Meyen var. clathratum Ghod. Figs. 2, 7, 

 8 [Meyen 1828 pag. 772] [Ghodat 1902 pag. 225]. This species is 

 found, as already mentioned, as a constant element of the plank- 

 ton in Bure Sø by the village Slangerup in North Sealand. 



The arrangement of the bristles is in the following manner: 

 at the points of the marginal cells, there are tufts of 2 — 4 great 

 bristles, often to be seen without preparation by the aid of a 

 high magnification; and from the junctions of the inner cells with 

 one another or with the marginal cells, bristles project at right 



Fig. 8. Pediastrum simplex Meyen. A coenobium seen from the edge. 

 Tannic acid vesuvin. Seibert Obj. V., Oc. I, (x380). 



angles to the plane of the coenobium. In the cilia-staining pre- 

 parations it looks as if the bristles from the junctions between 

 two marginal cells are projecting in the plane of the coenobium, 

 but the dark-ground illumination and the 'colouring with tannic 

 acid vesuvin show the fact as stated. 



Are specimens of this species treated with eau de Javelle, ap- 

 pears, as mentioned above, a distinct hollow at the point of the 

 marginal cells. It is deeper in this species than in any other, and 

 the knob that fills it, when the alga is living, is therefore here 

 unusually distinct (vide figs. 7, 8). At the junctions of the cells it 

 is not always possible in the cilia-staining preparations to see any 

 dark coloured body, from which the threads may project, but I 

 have not tried other stainings to examine into this point. 



