C YANOPHTCE^. 



219 



288. — The genera Protococcus, Chlorococcum, and one or 

 two others, are probably to be placed near the Palmellaceffi, 

 although their autonomy is doubtful also. They are all 

 unicellular in the strictest sense of the term, and reproduce 

 mainly by fission. In their resting stage they are spheroidal ; 

 in their motile stage they are pro\'ided with two cilia. The 

 latter form is said to arise from the former by internal cell- 

 division, which results in the production of "gonidia" of 

 two sizes, the larger being termed macrogonidia, and the 

 smaller microgonidia. 



These organisms are common in shallow pools, in the gut- 

 ters of roofs, and on the wet earth. 



(a) On account of their ready perishability, Protophytes are scarcely 

 found in a fossil state. Schimper records a species of Nostoc from the 

 Tertiary. 



(6) The relationship of the classes of the Protophytes may be indi- 

 cated by the following diagram : 



(c) For an account of the structure of Protococcus, with directions 

 as to methods of study, see Arthur, Barnes and Coulter's " Hand- 

 book of Plant Dissection," p. 33. 



{d) In the study of the Cyanophycese, and of other "fresh- water 

 algsB," the student will find Rev. Francis WoUe's "Fresh- water 

 Algae of the United States" (1887) of great value. 



Arkangement of the Classes of Protophyta. 



Cyanophycese 



Myxomycetes. 



Schizomycetes. 



