78 



Chlorophycece 



observed any pyrenoids in the chloroplasts of this genus. Borzi 1 

 has recently described the formation of zoogonidia. 



The cells of G. protogenita Kiitz. (fig. 22 C E), which is the typical species 

 of the genus, only reach a diameter of 3 4'5 p.. The plants are very rare and 

 occur in bogs or boggy pools. 



Genus Geminella Turp., 1828 s ; Lagerh., 1883 3 . [1 Planctonema 

 Schmidle, 1903.] This genus is scarcely to be distinguished from 

 Hormospora Breb. except for the arrangement of the cells in pairs. 

 The cells are fairly remote, are enveloped in a thick mucous coat, 

 and after division the daughter-cells separate only very slightly. 

 The chloroplast is exactly as in Hormospora. The cells of some 

 of the filaments occasionally develop thick brown cell-walls arid 

 become resting akinetes. 



G. interrupta Turpin (fig. 23 A C) is the only known species and it is 

 rarely found in the British Isles. The cells are 6'5 7 /j. in diameter. It 

 would perhaps be more correct to unite the genera Geminella and Hormospora, 

 the former having priority. 



It is impossible to find any 

 generic characters sufficient to 

 separate Planctonema Schmidle 

 from Geminella or Grlveotila. 



Genus Radiofilum Schmidle, 

 1894. The filaments are simple, 

 sometimes short and fragile, some- 

 times long and flexuose, and they 

 are enclosed in a considerable 

 mucous sheath, which exhibits 

 a more or less distinct radiating 

 fibrillar structure. The cells are 

 globose, ellipsoid, or sublenti- 

 cular, free and distant or joined 

 by a narrow hyaline bridge, always 

 forming moniliform filaments 

 after the manner of those of the 

 Nostocacese. In each cell there 

 is one chloroplast containing a 

 single pyrenoid. In one species 

 the cell-wall is composed of two 



H 





 I 



Fig. 23. A C, Geminella interrupta 

 Turp. ; A and B, from near the Lizard, 

 Cornwall ( x 440) ; C, two resting aki- 

 netes from Glen Tummel, Perthshire, 

 Scotland ( x 350). D, RadiolUnm flaves- 

 cciis G. S. West, from Wicken Fen, 

 Cambridgeshire (x440). 



1 Borzi, ' Studi Algologici II.' 



Turpin in Mdm. du Mus. d'hist. nat. 1828, torn, xvi, p. 329, t. 13, f. 24. 



3 Lagerh. in Ofvers. af K. Vet.-Akad. Forh. 1883, no. 2. 



