WISCONSIN PHYTOPLANKTON 



PEDIASTRUM DUPLEX Meyen. PL 46, Figs. 14-16. 



Nova Acta Phys. Med. Ac. Caes. Leop.-Carol. Nat. Cur. 14*: 772, pi. 43, figs. 

 6-20. 1829. 



Coenobia of 8-16-32-64^128 (generally 16-32) cells, with small lens- 

 shaped perforations between the cells. Interior cells more or less rec- 

 tangular, not in contact with one another in the central portion of the 

 side walls. Inner half of marginal cells similar to interior cells, outer 

 half prolonged into two short truncate processes. Cell wall smooth. 

 (Facultative Planktont). 



Diam. cells 11-21 p.. 



Balsam (rrr), Bear (2) (r), Birch Island (rr), Browns (rr), Catherine (rr), 

 Center (r), Clam (rrr), Cochrane (rr), Crawling Stone (r), Deer (rr), Des 

 Moines (rrr), Diamond (rrr), Eagle (r), Fishtrap (rr), Found (rr), Fowler 

 (rr), Helen (1) (rr), High (rr), Kawaguesaga (rr), Kegonsa (r), Kitten (r), 

 Lac la Belle (r), Lindy (rr), Little Bass (2) (rr), Little Bear (r), Little 

 Crooked (r), Little Rice (2) (rr), Long (3) (rrr), Lost (rr), Mendota (sss), 

 Mercer (rr), Meronk (rrr), Monona (c), Nagawicka (rr), Nancy (sss), Nica- 

 boyne (rrr), North Twin (rr), Oconomowoc (rr), Okauchee (rr), Pardee (rr), 

 Pokegama (1) (ss), Pokegama (2) (rr), Poor Farm (r), Poplar (rrr), Round 

 (1) (r), Round (2) (rr), Sand (4) (sss), Sishebogema (rr), Soft (r), South 

 Turtle (sss), Taylor (rr), Tenderfoot (r), Tied Canoe (rrr), Upper Nemahbin 

 (rr), Waubesa (ccc), White Sand (rrr), Wildcat (sss), Wild Goose (rrr), 

 Winnebago (ss),Wolf (sss). 



In many cases the marginal cells of this species and the varieties 

 clathratum, reticulatum and gracillimum have a tuft of long hyaline 

 setae at the apex of the projections. Their function is to give buoyancy 

 to the coenobe when living under pelagic conditions. Petersen (Bot. 

 Tids. 31: 161-176. 1911) has been able to demonstrate their presence 

 in other species by means of stains. 



var. CLATHRATUM (A. Braun) Lagerheim. PI. 47, Figs. 1-3. 

 Ofvers. Kgl. Vet.-Ak. Forh. 89, No. 2: 56. 1882. 



Cells more deeply emarginate and perforations of disc larger. (Fac- 

 ultative Planktont). 

 Diam. cells 12-22 p. 



Balsam (rr), Bear (3) (rr), Bear Trap (rr), Beaverdam (sss), Big Butter- 

 nut (rr), Blake (r), Bloom (rr), Camp (ss), Catfish (rr), Catherine (rr), 

 Chetek (s), Cranberry (rr), East (rrr), Fish (s), Horseshoe (1) (rr), Horse- 

 shoe (2) (rr), Lac du Flambeau (rrr), Lac la Belle (r), Little Bass (2) (ss), 

 Little Butternut (r), Little Wood (rrr), Long (1) (rrr), Loveless (sss), 

 Lower Turtle (r), Mary (r), Mendota (r), Middle McKenzie (s), Mud (2) (rr), 

 Mud (3) (sss), Nancy (r), Okauchee (rrr), Old Taylors (rrr), Fokegama (1) 

 (r),Rice (1) (es), Round (2) (rr),>Sand (3) (rr), Sand (4) (r), Spirit (sss), 

 Upper Turtle (sss), Wapagossett (rr), White Ash (r). 



