HOW TO KNOW THE FRESH-WATER ALGAE 



434a Groups of cells inclosed in concentric layers of mucilage; colonial 

 investment intermingling (confluent) with sheaths of other groups 

 and so forming gelatinous masses, mostly on moist substrates; 



sheaths showing definite concentric rings. Fig. 315 



GLOEOCAPSA 



.;:-■'->. Fig. 315. Gloeocapsa punctata Naeg. 



: '/jr*" ■■ '•' "©©)'■'• ®- This is a genus in which globular 



W..!%/( ^"Tgfc -^ cells are inclosed, many 'famiHes' to- 



'^/^^"/XS \ gether within gelatinous masses of con- 

 W;i @.Vx?" N :'i siderable size. A common habitat is 

 Wi^VA/ipfv'J the surface of moist rocks and cliffs, 

 rS\"<--' VSJ£v -->--v '^. ' soil in greenhouses, moist cement work, 

 -.;,- <-::..s etc Cells, pairs of cells, or clusters 



Figure 315 Q l ce \\ s are mc losed in concentric lay- 



ers of mucilage. Many species, especially when few cells are in- 

 volved, can scarcely be differentiated from Chroococcus (Fig. 316) and 

 there is a disposition among some specialists to place the two genera 

 together. 



434b Colonial mucilage not intermingling with that of other colonies; 

 families of cells separated from one another, usually free-floating 

 but commonly inhabiting soil and moist substrates in aerial situ- 

 ations; colonial sheath usually without conspicuous concentric 



rings. Fig. 316 CHROOCOCCUS 



/s=5f=^/^*p\ Fig. 316. a, Chroococcus Prescottii 



Q^y^tP Drouet & Daily; b, C. limneticus 



K^r^pK) var - distans G. M. Smith; c, C. 



^ viA^y - limneticus Lemm. 



There are numerous species in 

 this genus, many of them inade- 

 quately described and differenti- 

 al} ated. The genus is separated from 

 fy^JuC^) Gloeocapsa (Fig. 315) mostly on 

 ^t_J ^ the basis of the fewness of cells 

 b & involved in a colony and by the 

 Figure 316 fact that 'families' of cells are not 

 all inclosed in a common lamellated mucilaginous matrix. The 

 colonies are usually composed of no more than 16 cells and more 

 commonly of but 4, 8 or 12 cells. A few species are definitely plank- 

 tonic but others occur attached to aquatic substrates or form films on 

 aerial surfaces. C. turgidus (Kuetz.) Naeg. is a large species in which 

 cells occur in 2's and 4's within a stratified envelope and is one that 

 is invariably found in desmid habitats where the water is acid. 



435a (430) Cells arranged to form a flat plate 436 



435b Cells forming irregularly globular or oval colonies 437 



180 



a 



