476 University of California Publications in Botany [Vol. 6 



Brachytrichia Quoyi Guernsey, Notes on Mar. Alg., 1912, p. 195; 

 Collins, Holden and Setchell, Phyc. Bor.-Amer. (Exsicc), no. 2106, 

 type (not of Bornet and Flahanlt). 



Brachytrichia Quoyi was accredited to our coast by Bornet and 

 Flauhault (Rev. II, 1886, p. 373) on the authority of Grunow. It 

 has not been possible in this study to compare our plant with the type 

 of Agardh's Nostoc Quoyi from the Mariana Islands, nor with Zanar- 

 dini's Brachytrickia rivularioides from Sarawak, Borneo, but compari- 

 son has been made with B. Quoyi from Woods Hole, Massachusetts, 

 which, as has been suggested by Collins, probably was introduced 

 some years ago from some of the southern islands through the instru- 

 mentality of guano ships or other human agencies. It has also been 

 compared with material of the same species from the Philippine 

 Islands. 



Our plant is much smaller than those of B. Quoyi from Woods 

 Hole and from the Philippines, the specimens at Woods Hole some- 

 times measuring up to 7 cm. in diameter. The largest specimen yet 

 seen of B. a/finis measures about 2 cm. in diameter, the greater majority 

 being less than 1 cm. It is also much more firm and cartilaginous, 

 more profusely lobed and saccate. The cells are in general slightly 

 larger and the filaments more profusely branched. 



The branching of filaments in Brachytrichia is unique. The 

 filaments at first are more or less horizontal. At certain points in 

 them lateral loops, sometimes only a few cells long, at other times 

 many cells long, are formed (pi. 41, fig. 27). One cell at the end of 

 the loop divides lengthwise cutting off a cell which becomes the basal 

 cell of a branch which develops toward the surface of the frond, giving 

 the appearance of dichotomous branching, although virtually a single 

 filament gives rise to a single lateral branch at certain intervals. 

 Occasionally after the cortical portion of the thallus becomes dense, 

 branches develop without the formation of loops (pi. 41, fig. 28). This 

 is in reality true branching, for the erect filament is connately joined 

 to the parent filament. Soon a heterocyst is formed near the base of 

 the erect brancli and eventually the upper part develops into a Calo- 

 thrix-like filament tapering to a very delicate hairlike point. Other 

 intercalary heterocysts may appear. These masses of erect parallel 

 filaments form the cortical portion of the thallus. 



The genus Brachytrichia has hitherto been placed among the 

 Rivulariaceae, on account of the erect, tapering trichomes which occa- 

 sionally 7Tiay become detached from the parent trichomes and thus 



