52 WISCONSIN PHYTOPLANKTON 



three times as long as they are broad, generally with numerous pseudo- 

 vacuoles. Heterocysts cylindrical, with straight or slightly convex sides, 

 without a distinct polar nodule. Spores elongate, cylindrical, with 

 rounded or somewhat flattened ends, generally some distance from the 

 heterocysts. ( Euplanktont) . 



Cells 4r-6 p. broad, 5-15 //. long ; heterocysts 5-7 M broad, 7-20 /x long ; 

 spores 6-8 p. broad, 35-80 p long. 



Amicoy (aa), Balsam (ss), Bear (3) (rr), Beaverdam (rr), Big (r), Big 

 Butternut (rr), Birch (1) (c), Bone (rr), Camp (r), Catfish (sss), Center 

 (rrr), Chetac (aaa), Cranberry (ss), Crawling Stone (rrr), Deer (rrr), Dun- 

 ham (rr), Found (rr), Fowler (rr), Granite (a), Green (2) (ss), Half Moon 

 (sss), Hillman (sss), Hooker (cc), Horse (rrr), Horseshoe (1) (rr), Island 

 (c).Kawaguesaga (ccc), Kegonsa (cc), Lac la Belle (rr), Little Bass (2) (rr), 

 Little Butternut (s), Little Rice (1) (s), Little Wood (rr), Long (3) (rr), 

 Lost (ss), Loveless (ss), Lower Nashotah (rr), Mendota (s), Mud (3) (rr), 

 Nagawicka (rr), North Twin (rrr), Oconomowoc (rr), Okauchee (rr), Par dee 

 (cc), Pewaukee (rr), Pike (rr), Plum (r), Pokegama (2) (rrr), Pokegama 



(3) (aaa), Poplar (rrr), Prairie (aaa), Reserve (rr), Rice (1) (ss), Round 

 (1) (sss), Round (2) (ss), St. Croix (ccc), Sand (1) (r), Sand (3) (r), Sand 



(4) (r), Sahford (sss), Shell (rrr-), South Turtle (sss), Squirrel (a), Streitor 

 (rr), Tied Canoe (sss), Upper Nashotah (rr), Upper Nemahbin (r), Upper 

 Turtle (rr), Vermilion (r), Waubesa (s), White Ash (rr), Whitefish (rr), 

 White Sand (ss), Winnebago (r). 



When the alga occurs in any quantity the lake appears to be filled 

 with small pieces of macerated grass and it is one of the few plankton 

 genera that can be determined without the aid of a microscope. The 

 colony is so opague that the heterocysts cannot be seen while the colony 

 is intact but after a mount has been standing a few minutes the colonies 

 begin to dissociate into the component filaments and observation of the 

 heterocysts and spores is then an easy matter. The colonies are fre- 

 quently sterile and it is generally only during the colder months of the 

 year that there is a formation of spores. 



Family RIVULARIACEAE. 



Filaments rarely solitary, generally forming sessile or free-floating 

 spherical, hemispherical, or amorphous colonies. Trichomes gradually 

 attenuated from a broad basal cell to a hair-like apical cell. Sheaths 

 copious, homogeneous or lamellated, hyaline or colored, firm or gelat- 

 inous; enclosing one or more trichomes. Cells hemispherical, spheri- 

 cal, or disciform with convex sides at the basal portion of the trichome, 

 elongate cylindrical in the apical region. Cell contents variously col- 

 ored ; homogeneous, granulose, or with numerous pseudovacuoles. Trich- 

 omes simple or with "false branching". Heterocysts solitary; usually 



