10 University of Calif ornia Piihlic^tions in Bot(uiij f'^^oi- ^ 



The gt-'ims Chruococcua, as establislied by Naegeli in 1849, was dis- 

 tinctly set off and used in practically the exact sense of the present 

 time. The type of the genus, as designated by Naegeli, is the Pleuro- 

 coccus rufcscois Breb. published as a manuscript name by Kuetzing 

 (1846, p. 9) under his Protococcus riifescens. Some difference of 

 oi)inion seems to exist as to the present status of this type. Raben- 

 horst (1868, p. 28) uses the name of de Brebisson in his account of the 

 "Chlorophyllophyceae" and West (1916, p. 93) restores the genus 

 Protococcus and reckons P. rufescens (Breb.) Kuetz. among the 

 Chlorophyceae. An examination of the type specimen in Herb. 

 Kuetzing, for which privilege we are indebted to Dr. Weber-van Bosse, 

 demonstrates clearly that the plant of de Brebisson is a Chroococcus in 

 the sense of Naegeli. Naegeli, hoAvever, evidently derived his concep- 

 tion of the genus from Chroococcus rufescens var. turicensis Naeg., as 

 described and figured bj'- him (1849, p. 46, pi. 1, fig. 1). All of the 

 stages figured bj' Naegeli are to be found in the type material, so that 

 it seems likely that no considerable differences are to be found between 

 the species and its variety. From Naegeli 's figures and from the 

 species other than the type referred to Chroococcus by Naegeli, there 

 can be no doubt as to his conception of the genus. 



The genus Chroococcus is compared by Naegeli (1849, p. 53) with 

 Gloeocapsa Kuetz. and Aphanocapsa Naeg., who states that while they 

 are closeh^ related to one another, they are distinctly set off from the 

 other genera whose descriptions follow in Naegeli 's monograph. The 

 whole difference, as Naegeli says, lies in the fact that in Chroococcus 

 the teguments are thin, in Gloeocapsa thick and firm, while in Aphano- 

 capsa they are thick but so soft that they coalesce into a structureless 

 jelly. All other characteristics are secondary, and there occur forms 

 which might with equal reason be referred to one or another of the 

 three genera. It may seem best, at some time, to unite Chroococcus 

 with Gloeocapsa, but, for the present, we shall follow the custom and 

 retain both as distinct genera. 



Chroococcus turgidus (Kuetz.) Naeg. 



Cells spherical or ellipsoidal when single, or angular from mutual 

 compression when in colonies, 1-4, rarely 8, in colonies, 13-25/x, rarely 

 40/x diam., tegument comparatively thick, often somewhat lamellate, 

 hyaline, cell wall thin, not distinct; protoplast vivid blue-green, 

 homogeneous, or becoming faded more or less, and granular. 



