>j WISCONSIN PHYTOPLANKTON 



: .) i 



-.r.ature. Cells 1'inate to arcuate, never sickle-shaped; gradually taper- 

 mg to a sharp point. Chloroplast single, parietal on convex side of cell ; 

 without a pyrenoid. (Facultative Planktont). 

 Diain. cells 1.5-2.6 p. Distance between apices 15-18 p.. 



DeviLs (1) (rr). 



The cells of this species are quite like those of Scenedesmus acumi- 

 natus (Lagerheim) Chodat but their organization in the colony is quite 

 different. West has recently investigated an organism which he con- 

 siders identical with the Selenastrum acuminatum described by Lager- 

 heim. I have obtained West's organism in pure culture and find that 

 the cell shape and colony organization is as he describes. The fortunate 

 rediscovery of Lagerheim 's species from the plankton of Horse Lake 

 shows that in the organization of the colony it is a Scenedesmus and 

 that Chodat is entirely correct in removing the species from Selenast- 

 rum. The organism that West found is, on the other hand, a true 

 Selenastrum but is not the species which Lagerheim erroneously re- 

 ferred to Selenastrum. 



ANKISTRODESMUS Corda 1838. 



Cells acicular to fusiform ; straight, lunate, or sigmoid ; ends of ceils 

 gradually tapering to a point; solitary or loosely aggregated without 

 order in temporary colonies that are not embedded in a gelatinous en- 

 velope. Chloroplast single, parietal, sometimes fragmented into small 

 pieces ; with or without a pyrenoid. 



Reproduction by the formation of several autospores in any cell. 



KEY TO THE SPECIES. 



Cells twisted around one another A. SPIRAUS 



Cells not twisted around one another A. FALCATUS 



ANKISTRODESMUS FALCATUS (Corda) Ralfs. PI. 32, Fig. 1. 



Brit. Desmidieae 180, pi. 34, figs. 3"-3b. 1848; G. S. West, Brit. Freshw. Algae 

 223, fig. 94A. 1904. 



Cells acicular to narrowly fusiform, tapering very gradually to acute 

 apices, lunate or slightly arcuate. Length 12-24 times the diameter. 

 Seldom solitary, generally loosely associated in fasiculate bundles. 

 Chloroplast single, generally without pyrenoids. (Facultative Plank- 

 tont) . 



Diam. cells 1.5-3.5 /* ; length 20-80 ^ 



Fence (rrr), Half Moon (rrr), Horse (rr), Kawaguesaga (rrr), Lac du 

 Flambeau (rrr), Little Crooked (rr), Lost (rr), Oconomowoc (rrr), Pine 



