Rivulariacese 



45 



form an expanded stratum on wet rocks and submerged stones (fig. 35). In Rivularia the 

 filaments are disposed to form subglobose or hemispherical, attached masses, sometimes 



Fig. 34. A and B, Stigonema minutum Hass. ; A, xlOO; B, x 440. C E, St. ocellatum 

 (Dillw.) Thur. ; C, xlOO; D and E, x 400. h, heterocyst. 



Fig. 35. A and B, Calothrix parietina (Nag.) Thur. C, Dichothrix interrupta W. & 

 G. S. West. D, D. Orsiniana (Kiitz.) Born, & Flah. All x 420. 



gelatinous and sometimes incrusted with lime. In Glceotrichia, which occurs largely in 

 the plankton, the gelatinous mass is usually free-floating. The genus scarcely differs from 

 Rivularia, except in the formation of large cylindrical resting-spores. In Homceotkrix 

 and two other genera there are no heterocysts. 



