Pleurococcacece 201 



Family 5. PLEUROCOCCACE.E3. 



The plants of this family are either unicellular or composed of 

 very short, slightly branched filaments, which consist of few cells 

 and are never attenuated to form hairs. The short filaments 

 are generally creeping and are often compacted into pseudo"- 

 parenchymatous masses. Considerable polymorphism is exhibited 

 by the different members of this family. 



The cells are variable in outward form and contain one or 

 several parietal chloroplasts, with or without pyrenoids. 



Multiplication takes place by division in two or three directions, 

 and asexual reproduction occasionally occurs by the formation of 

 biciliated zoogonidia. Gametes are rarely produced. 



In the two most frequent genera of the family, namely Plenro- 

 coccus and Trochiscia, the cells are more or less globose and occur 

 aggregated in large masses ; the former prefers a subaerial habitat 

 whereas the latter prefers an aquatic existence. In Hormotila 

 there is a marked increase in thickness of the cell-wall at one side 

 only, branched colonies of cells being formed by the more or less 

 complete fusion of these remarkable lamellose excrescences. 

 Protoderma is usually epiphytic, and its short cell-filaments 

 commonly assume a pseudoparenchymatous character ; it is 

 placed here on account of its close resemblance to certain of the 

 more uncommon states of Pleurococcus. 



The cell-walls are usually very strong and firm, and the cells 

 are associated to form indefinite colonies or irregular aggregations. 

 This fact, and the complete absence of autospores, separate the 

 Pleurococcacese from the Protococcaceae. 



Chodat 1 includes in this family the genera Microthamnion and 

 Gongrosira, Alga? which I have referred to a distinct family the 

 Microthamniacese of the Chastophorales. There is considerable 

 resemblance between certain states of Pleurococcus and the young, 

 germinating plants of Microthamnion, but the latter genus has 

 reached a much higher stage of development than is ever attained 

 by forms of Pleurococcus. It is very probable that the family 

 MicrothamniaceaB has had a direct origin from certain of the 

 Pleurococcaceaa. 



1 Chodat in Beitriige zur Kryptogamenflora der Schweiz, Bd i, Heft 3, Berlin, 

 1902. 



