26 WISCONSIN PHYTOPLANKTON 



Class MYXOPHYCEAE. 



Cells solitary, in colonies of definite or indefinite shape, or in fila- 

 ments but always surrounded by a gelatinous to tough envelope which 

 is generally hyaline but may be colored. Plants living a free-floating, 

 sessile, epiphytic or endophytic existence. Cell shape various; spheri- 

 cal, hemispherical, ovoid, bacilliform, disciform or angular. Cells with 

 the coloring matter localized at the periphery but not in definite, visible 

 chromatophores. Color of cells typically blue-green but at times grey, 

 yellowish, reddish, brownish or nearly grass-green. The color variation 

 being due to different amounts of the three component pigments, caro- 

 tin, chlorophyll, and phycocyan; the latter being found only in this 

 class of plants. Cells containing a single nucleus of a primitive type 

 (the central body) that contains linin and chromatin but is without a 

 membrane or nucleole. 



Reproduction always asexual, either by vegetative division of cells; 

 fragmentation of the filaments into smaller portions (hormogones) 

 which may move a short distance by spontaneous movement and then 

 come to rest; or by special non-motile reproductive bodies (gonidia and 

 resting spores) . 



KEY TO THE ORDERS. 



Cells solitary or in colonies, never in filaments COCCOGONEAI<ES 



Cells in simple or branched filaments HOEMOGONEAUBS 



Order COCCOGONEALES. 



Cells rarely solitary, generally in colonies of regular or irregular 

 shape, and with the cells definitely or indefinitely arranged within a 

 copious gelatinous envelope. Colonies living a free-floating, sessile, 

 epiphytic or endophytic existence. Cells differentiated into a basal 

 and distal portion or without such differentiation. Cell shape various ; 

 spherical, ovoid, cylindrical, acicular, or angular. 



Asexual reproduction by vegetative division of the cells or, in rare 

 cases, by a division of the cell contents into non-motile gonidia. Rest- 

 ing cells and sexual reproduction unknown. 



There are two families in the order only one of which, the Chroococ- 

 caceae, is found in the plankton. 



