CHROOCOCCUS Naegeli 1849, p. 45 



One-celled, or an association of 2-32 spherical, hemispherical or 

 ovate individuals, either free-floating, adhering to submerged sub- 

 strates, or forming expansions in moist aerial habitats; each cell with 

 a sheath which may be distinct from or (as in most planktonic 

 species) confluent with the common mucilage investing a group of 

 cells; several generations of sheaths present as a result of successive 

 cell divisions; sheaths either hyaline or ochraceous; cell contents 

 homogeneous or granular, not vacuolate, light to bright blue-green, 

 olive-green, or yellowish. 



The sedentary species, especially, should be compared with 

 Gloeocapsa, a genus which in some conditions and stages of develop- 

 ment might be confused easily with Chroococciis. Gloeocapsa forms 

 attached, gelatinous masses on either submerged substrates or, more 

 commonly, in aerial habitats. In Gloeocapsa, many more cells are 

 associated in families and clusters of famihes than in Chroococcus; 

 the individual cell sheaths are usually thick and conspicuous, and 

 the gelatinous matrix in which the cells are embedded is formed of 

 several concentric layers. A small, isolated, and little-developed 

 clump of Gloeocapsa resembles certain species of Chroococcus. It 

 is desirable, therefore, to see a number of plants in a collection 

 before attempting determinations. 



Key to the Species 



1. Cells large, 13-70^ in diameter 2 



1. Cells smaller, 1.5-10/x in diameter - 3 



2. Maximum diameter of cell, including sheath, 50;^ — C turgidus 



2. Ceils larger, diameter 67-70At including the sheath C. giganteus 



3. Colonial mucilage or individual cell sheaths lamellate 4 



3. Colonial mucilage or individual cell sheaths not lamellate - 5 



4. Cells arranged in cubical ( sarciniform ) packets C. PrescoUii 



4. Cells not in cubical packets - C. varitis 



5. Cells arranged in cubical packets of from 4-8, or in multiple 



packets of 32 cells in Sarcina-like families C. Prescottii 



5. Cells not arranged in cubical packets 6 



6. Colonies free-floating in the euplankton 7 



6. Colonies adhering to substrates, or entangled 



among other algae in tychoplankton 9 



7. Colony of many cells within a homogeneous sheath, 



cells 2S/1 in diameter C. minimus 



7. Colony of 24 or fewer cells in a homogeneous sheath, cells 



usually more than S/j. in diameter ^ 



8. Cells S-4.5 fi in diameter, arranged at 



some distance from one another.- — C. dispersns 



8. Cells 6-12-(22)m in diameter, arranged close together C. limneticus 



[446 ] 



