100 University of California Piihlications in Botany [Vol.8 



N.W. Araer., 1903, p. 197 ; Collins, Holden, and Setchell, Phyc. Bor.- 

 Amer. (Exsicc.) nos. 1212, 2104. 



This species presents a great varietj' of variations. As interpreted 

 by Thuret and by Bornet and Flahault the variation in the diameter 

 of the filaments is from 12/i, to 40jli. A variation so great as this has 

 not been reported in any other species of the genus. It may be that 

 we are dealing here with a heterogeneous group. The heterocysts are 

 basal and intercalary, varying from one to several in each position. 

 In its multiplicity of branching there is great diversity. Some collec- 

 tions have the filaments almost wholly without branching. This is 

 considered to be the typical form. In other collections there are 

 intermingled specimens without branches and those with profuse 

 branching approximating to such species as C. prolifcra Flah., C. 

 fasciculata Ag., and even to the extreme represented by C. vivipara 

 Harv. 



9. Calothrix rectangularis S. and G. 



Plate 6, fig!. 21 



Filaments simple or occasionally sparsely branched, attached at 

 the base to various other algae, prostrate when j-oung, soon becoming 

 erect, 400-500/x, long, 24-28/x diam. at the base ; trichomes 16-18ju, diam. 

 at the base, tapering gradually upward nearly to the apex, then rather 

 abruptly ending in a short hair; cells 2-4/x, long, protoplasm finely 

 granular, pale blue-green; sheath hyaline when young, changing to 

 light yellow with age, strict at the apex; heterocysts basal and inter- 

 calary-, the basal spherical to subconical, the intercalary cylindrical, 

 usually single, near the base of the trichome, 18-25/x long, the same 

 diameter as the trichome. 



Epiphytic on various species of marine algae, near low-tide level. 

 East Sound, Orcas Island, Washington. 



Setchell and Gardner, m Gardner, New Pac. Coast Alg. Ill, 1918a, 

 p. 472, pi. 40, fig. 21. 



This species comes within the range of measurements stated by 

 Bornet and Flahault (Rev. I, 1886, p. 359) for the diameter of the 

 filaments of C. Crustacea Thuret with which it seems to be most closely 

 related, the filaments are, however, much shorter than the measure- 

 ments given for that species. The small size, the habit of growth on 

 other algae, the presence of cj'lindrical, intercalary heterocysts always 

 near the base of the trichomes, the infrequencj^ of branching, and the 



