— 174 — 



11. Pediastrum duplex Meyen var. clathratum 

 A. Br. Tannic acid vesuvin (x 730). 



I have found this var. in Bagsværd Sø and Bastrup Sø in 

 North Sealand. 



The arrangement of the bristles is the same in ah varieties, 

 but, as usual, there is often a great difference between the speci- 

 mens. In this respect there is moreover a great conformity with 



the preceding species; only has 

 the P. duplex two tufts on each 

 marginal cell viz. one on each 

 of the two cell processes. Their 

 hollows are not so deep as 

 those of the preceding species 

 and are much like a bowl 

 (Fig. 1, 11). 



The number of bristles in 

 a tuft differs, and I have coun- 

 ted from 5 — 30; but, as I have 

 already mentioned, it is very 

 difficult to give definite num- 

 bers. Also the thickness of 

 the bristles is very difficult to indicate exactly, but it seems not 

 to exceed 0-4 ju. 



Often their length is 40 p.. 



I have bristled specimens from Esrom Sø, Bagsværd Sø, Birke- 

 rød Sø, Bastrup Sø and Bure 

 Sø, from the pond of the 

 Botan. Garden and 8 other 

 ponds, that is to say from 

 whereever I have found 

 this species in any greater 

 number. 



Pediastrum Boryanum 

 (Turp.) Menegh. Fig. 12. 

 [Ghodat 1902 pag. 228]. 



The arrangement of the 

 bristles in this species is the 

 same as in the preceding 

 one, but often the tufts pro- 

 jecting at right angles to the 

 plane of the coenobium are 

 absent. There is often found from 



Fig. 12. Pediastrum Boryanum (Turp.) Menegh. Löfflers 

 method (x 730). 



10 — 20 bristles in every tuft. 



