150 WISCONSIN PHYTOPLANKTON 



TETRADESMUS G. M. Smith 1913. 



Colonies free-floating, four-celled, rarely two- or three-celled. Cells 

 in two planes with two cells in each plane and joined along the long 

 axes when the colony is viewed from the side. Viewed from the top 

 cells quadrately arranged. Cells elliptic-fusiform to broadly elliptic, 

 with outwardly divergent or straight apices. Chloroplast single, pari- 

 etal and laminate or completely filling the cell ; pyrenoid single, central 

 or eccentric. 



Reproduction by autocolony formation in any cell of the colony, the 

 young coenobia being liberated by a rupture of the mother cell wall. 



TETRADESMUS WISCONSINENSIS G. M. Smith. PI. 37, Figs. 7-11. 

 Bull. Torr. Bot. Cl. 40: 76, pi. 1, figs. 1-2, 3-20. 1913. 



Cells elliptic-fusiform, apices attenuated and outwardly divergent. 

 Pyrenoids eccentric. (Facultative Planktont). 

 Cells 4-6 p. broad, 12-14.5 /* long. 



Blake (rrr), Mendota (rr), Nancy (rrr). 



SCENEDESMUS Meyen 1829. 



Coenobe a flat (rarely curved) plate of ellipsoidal, ovoid, or acicular 

 cells with cell number always a multiple of two. Cells in lateral con- 

 tact and in one or two rows. Cell wall smooth, corrugated, granulate, 

 or spicate ; with or without marginal or lateral teeth or spines. Chloro- 

 plast single, parietal, and laminate in young cells; frequently filling 

 entire cell in older colonies ; pyrenoids single, central or eccentric. 



Reproduction by autocolonies from any or all cells of the coenobe, 

 the number of cells in the colony not necessarily the same as that of 

 the mother colony. 



KEY TO THE SPECIES. 



Walls smooth, without granulations, lateral ridges, terminal teeth or spines. 

 Cells acicular to broadly elliptic, with pointed ends. 

 Colony a flat plate. 



All cells in colony erect S. OBLIQUTJS 



Median cells erect, terminal cells lunate S. DIMOBPHTJS 



Colony a curved or twisted plate. 



Cells forming a curved surface S. ACTJMINATUS 



Cells alternately arranged with terminal cells not in the 



same plane as the others S. BEBNABDH 



Cells ovoid to cylindrical, with rounded ends. 

 Arrangement of cells a single linear or subalternating but 



never a double series S. BIJUGA 



Arrangement of cells a double linear series S. ABCUATUS 



