Ulvellese 



299 



irregular, and often massive. Except in Ulvella it contains a single pyrenoid. 

 The genus Ulvella is also peculiar in the fact that the ' cells ' have several 

 nuclei. 



Reproduction takes place by ovoid zoogonidia, which are biciliated in 

 Protoderma and Ulvella, but quadriciliated in Pringsheimia, Pseudulvella 

 (fig. 192 E) and Ochlochmte (fig. 193 C). As many as 30 zoogonidia may 

 arise in a zoogonidangium, and the latter, which are generally larger than 

 the vegetative cells, are developed only in the more central parts of the 

 thallus. The zoogonidia escape by an apical orifice or by the dissolution of 

 a large part of the wall of the zoogonidangium. 



Quadriciliated gametes are known in Pringsheimia. 



m 



c 



Fig. 192. A and B, Ulvella Lens Crouan. A, young plant, x280; B, central portion of the 

 thallus, x 750. C E, Pseudulvella americana (Snow) Wille. C, portion of thallus from 

 above, x 280 ; D, middle part of same in transverse section, x 820 ; E, zoogonidia, x 820. 

 (A and B, after Huber ; C E, after Snow ; from Wille.) 



The Ulvellese are mostly marine Algse ; the genera are : Ulvella Crouan, 1859 [inclus. 

 Dermatophyton Peter, 1886 (Sept.) and Epiclemidia Potter, 1886 (Nov.)] ; Pseudulvella 

 Wille, 1909 ; Protoderma Kiitzing, 1843, em. Borzi, 1895 [inclus. Entocladia Hansgirg, 

 1888] ; Pringsheimia Reinke, 1889 ; Pseudopringsheimia Wille, 1909 ; Ochloch&te Thwaites, 

 1849 ; Chxtobolus Rosenvinge, 1898 ; Arthroch&te Rosenvinge, 1898. 



All the genera are epiphytic except Arthrochsete, which is sometimes endophytic in 

 the thallus of Turnerella Pennyi (a red seaweed of the Rhodophyllidacese). One fresh- 

 water species of Chsetobolus Ch. lapidicola Lagerh. is found on stones in streams in the 

 north of Norway. Protoderma viride Kiitz. is a common freshwater Alga occurring as an 

 epiphyte on species of Lemna, Callitriche, etc. Pseudulvella americana (Snow) Wille is a 

 freshwater epiphyte of N. America. Ulvella involeens (Savi) Schmidle ( = Dermatophyton 



