Ulotrichacece 



79 



equal halves, but in others it is not. The cells multiply by division 

 which is preceded by a division of the chloroplasts and pyrenoids. 



The type species of the genus, JR. conjunctivum Schmidle 1 , has not been 

 observed from Britain. R. flavescens G. S. West (fig. 23 D) is a larger 

 species, with much longer flexuose filaments and broad elliptical cells ; the 

 diameter of the cells is 7 '5 10-5 p and the chromatophores are of a yellowish- 

 green colour. 



Genus Stichococcus Nag., 1849. [Hormococcus Chodat, 1902.] 

 The filaments are entirely or very largely aerial, and are composed 

 of cylindrical cells. They readily become disarticulated into frag- 

 ments composed of a few cells, the extremities of the terminal 

 cells being broadly rounded. There is one parietal chloroplast in 

 each cell, plate-like or more or less irregular in form, and occupying 

 as a rule only a portion of the cell-wall. A small pyrenoid is 

 present in each. In some of the aquatic forms of Stichococcus 

 flaccidus I have observed a fragmenta- 

 tion of the chloroplast (cf. fig. 24 B). 



The plants are propagated by 

 division of the cells and fragmen- 

 tation of the filaments, by akinetes, 

 and by zoogonidia. The latter are bi- 

 ciliated, have no pigment spot, and 

 arise singly from cells which are under- 

 going rapid division. 



This genus much resembles Ulothrix, 

 but its adaptation to an aerial existence 

 has caused a multiplication by dis- 

 articulation of the filaments and a 

 reduction almost to a unicellular con- 

 dition. This disarticulation often takes 

 place first on one side and then on the 

 other, giving a zig-zag appearance to 

 the disarticulated filaments. Klebs has 

 shown that it is facilitated either by 

 too much or too little nourishment. 

 The genus was well studied by Gay 2 . 



There appears to be no justification 

 whatever for Chodat's name "Hormo- 



Fig. 24. A, Stichococcus 

 bacillaris Nag., from Saltaire, 

 W. Yorkshire. B, S. flaccidus 

 (Kiitz.) Gay, from Barnes Com- 

 mon, Surrey. C, S. dissectus 

 Gay, from damp walls, London. 

 D, S. variabilis West & G. S. 

 West, from Bradford, W. York- 

 shire ( x 440). 



coccus. 



1 Schmidle in Flora, 1894, Heft 1, p. 47, t. vii, f. 4, 5. 



2 Gay, 'Becherches sur le devel. et les classif. de quelques Algues Vertes,' 

 Paris, 1891. 



