386 University of California Publications in Botany [Vol.7 



Zoosporangia occupy very niiu-li the same position in the filaments as 

 tlie irametangia. Tliey are subterminal, long-catenate, but seem to be 

 i"ornied more nearly simultaneously than are the gametangia. 



These plants are quite abundant on the blade of the host-plant at 

 Neah Bay. We have not observed it growing elsewhere, although the 

 host is abundant in the vicinity of the Strait of Juan de Fuca. They 

 are, however, very inconspicuous, forming small, more or less con- 

 tinuous expansions, barely recognizable when the host plant is wet. 



Pylaiella unilateralis sp. nov. 



Plate 42, figures 6-8 



Filamentis erectis per filamenta repentia, irregularia, plus minusve 

 ramosa afifixis, floccosis. leviter clavatis, 4-7 mm. altis, basi 19-22/x 

 diam., apieali 28-32/a diam., ramis in feme plerumque alternis spar- 

 sisque, superne secundis, e cellulis 1-2-plo longitudinaliter divisis 

 oriendis; cellulis 2-2.5-plo longioribus quam latis, basi cylindricis, 

 superne plus minusve quadratis doliiformibusque ; chromatophoris 

 tenuibus, irregulariter taeniatis et plus minusve connectis; zoospor- 

 angiis eodem tempore maturantibus, 7-12-catenatis, in ramulis plerum- 

 que terminalibus, sphaeroideis, 24-28/a diam. ; gametangiis ignotis. 



Growing on rocks in shallow pools, near high-tide limit. Sunset 

 Beach, near the mouth of Coos Bay, Oregon. Type, Gardner, no. 2748 

 (Herb. Univ. Calif., no. 207011), May, 1914. 



The secund branching, together with the longitudinal divisions of 

 the cells from which the secund branches arise forming a poly- 

 siphonous region are the chief distinguishing characteristics of this 

 species. The branching below is sparse, alternate or very rarely 

 opposite, and the branches are relatively long and attenuated. These 

 branches may give rise to terminal zoosporangia, or to a few short 

 alternate ramuli which in turn produce the zoosporangia. ]\Iany of 

 the main filaments become slightly enlarged toward their outer ends, 

 the cells becoming nearly quadrate, their walls thickened, and their 

 contents very dense. An average of about thirty-five cells, though 

 frequently as many as sixty-five, are thus transformed. A few cells 

 of the ends of the filaments are not transformed and soon disintegrate, 

 thiLs producing a distinctly clavate filament. The region of trans- 

 fonnation seems to be a new meristem of a peculiar nature. ]\Iauy 

 of the cells divide once or, less frequently, twice, by longitudinal planes 

 as a rule, but occasionally the dividing planes are at right angles 

 separating the cell into four parts. The unique feature resulting from 

 these divisions is the lack of further growth of the cells. Usually one 



