WISCONSIN PHYTOPLANKTON 89 



close phylogenetic connection between the Autosporaceae and the other 

 members of the Protococcales is, however, perfectly evident. 



KEY TO THE ORDERS. 



Cilia normally present throughout the whole life cycle VOLVOCALES 



Cilia present at time of reproduction only. 

 Cells in simple or branched filaments. 



Cells uninucleate, with a single laminate chloroplast ULOTRicHALjca 



Cells multinucleate, with one or more chloroplasts . . SiPHONOCLADiALEa 

 Cells solitary or in simple colonies, generally of microscopic 



size PBOTOCOCCALES 



Order VOLVOCALES. 



Cells normally ciliate and motile during the vegetative phases of the 

 life cycle. Solitary or organized into colonies of definite form that 

 generally contain a definite number of cells. Protoplasts rarely naked, 

 usually with a differentiated outer cellulose covering that may be par- 

 tially gelatinized. Shape of protoplast spherical, ovoid, disciform, 

 pyramidate, or irregularly radiate. Cells with a single cup-shaped to 

 irregular chloroplast, with or without pyrenoids ; with 2-4 cilia at the 

 anterior end ; generally with a disciform to bacillif orm eyespot, two to 

 several contractile vacuoles, and one nucleus. Palmella stages fre- 

 quently arising in the unicellular members. 



Asexual reproduction by division of cell contents into 2-16 zoospores ; 

 or a development of special, or all cells of the colony into autocolonies. 



Sexual reproduction by isogamous zoogametes; heterogamous zoo- 

 gametes ; or small motile antherozoids and large immobile oospheres. 



Many hold with G. S. West (Algae 151, 1916) "that it is very doubt- 

 ful if the Volvocineae have sufficient claims to be removed from the 

 Protococcales and elevated to a group of equal rank (the ' Volvocales') ". 

 There is a very close relationship between the "palmella" stage of 

 various unicellular Volvocales and the family Palmellaceae of the Pro- 

 tococcales. This represents to me, however, a close phylogenetic rela- 

 tionship between the two and not a justification for uniting in the same 

 order forms with mobile vegetative cells and those which are immobile. 



KEY TO THE FAMILIES. 



2 cilia at the anterior end of cells. 



Cells solitary CHLAMYDOMOIT ADACEAE 



Cells in definite coenobia VOLVOCACEAE 



4 cilia at the anterior end of cells CAOTERIACEAE 



