1919] Setchell-Gardncr : Mxjxophyccae 79 



it in his subtribe Lj-ngbyeae, next to Lyncjhya. Ilansgirg (1892, 

 p. 39) places it near Tolypothrix and Scytonema. In this he is fol- 

 lowed by Kirchner (1898, pp. 77, 78) and Forti (1907, p. 488). West 

 (1916, p. 43), however, follows Gomont. Since occasional false 

 branching is known in Symploca and even rarely in Lynghya, and 

 since some species of Plectancnm have few branches and none of them 

 have heterocysts, it seems best to place this genus as has been done 

 by Gomont and West. 



Key to the Species. 



1. Layer blackish or brownish green, trichomes 2-3. 5/a thick 



1. P. Battersii (p 79) 



1. Layer rose colored or reddish brown, trichomes 1.2-2/a thick 



2. P. Golenkinianum (p 80) 



1. Plectonema Battersii Gomont 

 Plate 1, fig. 1 



Filaments forming a black or dark green stratum, elongated, flex- 

 uous, abundantly and repeatedly false-branched ; branches usually in 

 pairs and smaller than the primary filaments; sheath hyaline, thick- 

 ened slightly in the primary filaments ; trichomes pale blue-green, 

 torulose, 2-3. 5/a diam., with long and gradually tapering apices ; the 

 older trichomes often very densely contorted within the sheath ; cells 

 up to four times shorter than the diameter, with homogeneous con- 

 tents; apical cell rounded. 



Growing on rocks near high-tide limit. Golden Gate, San Fran- 

 cisco, California. 



Gomont, Sur quelq. Oscill. nouv., 1899, p. 36; Collins, Holden and 

 Setchell, Phyc. Bor.-Amer. (Exsicc), no. 1712. 



The two members of the genus Plectonema credited to our coast 

 were found in the same localit}' and it is difficult at times to separate 

 them. Plectonema Battersii, as represented in no. 1712 of the Phyco- 

 theca Boreali-Americana, has slightly thicker trichomes and is de- 

 scribed as forming a black or brownish green layer. Unfortunately 

 the color of our specimens is not, at present, discernible. The branch- 

 ing in our specimens, while present, is not plentiful. But this species 

 and the next twine about other filamentous Myxophyceae and then 

 stream outward. The branching seems more common in younger speci- 

 mens and toward the base of the cluster of entangled filaments. This 

 is shown in specimens from the same locality but of another collection 

 than that distributed. 



