WISCONSIN PHYTOPLANKTON 65 



Class PHAEOPHYCEAE. 



Plants usually of macroscopic size and definitely shaped. Cells vari- 

 ously shaped and containing brown chromatophores in which a brown 

 pigment, phaeophycin, masks the chlorophyll. Cell wall not conspicu- 

 ously impregnated with silica and cells generally immobile in the vege- 

 tative phases. 



Asexual reproduction by vegetative cell division, aplanospores, and 

 zoospores. 



Sexual reproduction by isogamous zoogametes ; or heterogamous with 

 a fusion of zoogametes of unequal size, or a union of a large immobile 

 oosphere and a small motile antherozooid. 



All of the complex non-motile members of this class are marine and 

 only unicellular or simple colonial forms are found in fresh waters. 

 These freshwater forms have the motile phase dominant, as a rule, and 

 form the subclass Chrysomonadineae of the Phaeophyceae. Many 

 place all of the colorless or brown chromatophored motile unicellular 

 organisms in a class by themselves, the Flagellatae, but, as I have stated 

 elsewhere, the group of the Chrysomonadineae seems sufficiently related 

 to the Phaeophyceae to warrant uniting the two. 



Sub-class CHRYSOMONADINEAE. 



Cells with one or more definite, disciform, laminate, or reticulate, 

 golden-brown chromatophores. Cells free-swimming or sessile, solitary 

 or in colonies of definite to indefinite shape. Life cycle generally with 

 the motile phase dominant but sometimes developing into amorphous or 

 rhizopodial palmella stages. Cells either naked or with a gelatinous 

 to definitely constituted periplast. Individual cells with 1-2 anterior 

 or lateral cilia of equal or unequal length; 1-10 contractile vacuoles, 

 generally at the anterior end; with or without an eyespot; and with 

 one or more chromatophores. Symmetry of cells bilateral, not inter- 

 rupted by a lateral or longitudinal grooving. Nutrition holophytic or 

 fiaprophytic ; assimilation product leucosin or fat, never starch. 



Asexual reproduction by longitudinal or transverse division of cells. 

 Ilesting stages with heavy walls known in many genera. 



Sexual reproduction as yet unknown in the sub-class. 



