1925] Setchell-Gardner: Melcmophyceae 407 



cross-divisions of fructiferous cells have likewise been observed by 

 Borgesen (1920, p. 433) in P. fidvescens (Schousb.) Bornet, from the 

 Danish West Indies. We have also observed this condition highly 

 developed in forms of P. litt oralis. 



P. tenella evidently belongs to the Panthocarpus group of the 

 genus as established by Skottsberg (1915). The gametangia are 

 formed by the transformation of vegetative cells, usually beginning 

 relatively few cells back of the apices of the filaments, a considerable 

 number of cells transforming simultaneously. The transformation 

 continues in both directions until one-half to three-fourths of the 

 filament is converted into gametangia. The gametangia vary greatly 

 in size, some producing as many as thirty-two loculi from a single 

 assimilating cell. They may be continuous or discontinuous, certain 

 assimilating cells in the series not being transformed. The cell walls 

 in the formation of loculi frequently arc decidedly oblique. Zoo- 

 sporangia occupy very much the same position in the filaments as the 

 gametangia. They are subterminal, long-catenate, but seem to be 

 formed more nearly simultaneously than are the gametangia. 



The plants were fairly abundant on the blade of the host-plant at 

 Neah Bay. They are, however, very inconspicuous, forming small, 

 more or less continuous expansions, barely recognizable when the host- 

 plant is wet. We have not observed the species growing elsewhere, 

 although the host is abundant in the vicinity of the Strait of Juan 

 cle Fuca. 



4. Ectocarpus Lyngb. 



Fronds monosiphonous, composed of a creeping attaching portion 

 and an erect portion; creeping filaments irregular, more or less well- 

 developed, and more or less richly branched, usually entirely or 

 largely external to the substratum ; erect filaments usually abundantly 

 branched, naked, or corticated by descending rhizoidal filaments, 

 piliferous, or terminating in an acute or rounded cell, growth apical, 

 subapical or trichothallic ; chromatophores discoid or band-shaped, 

 with or without pyrenoids; zoosporangia on lateral branchlets, seldom 

 terminal, single, sessile or stalked; gametangia terminal on lateral 

 branchlets, sessile or stalked, exceptionally seriate and seldom even 

 intercalary, in some species dimorphic or polymorphic (mega- and 

 meio- gametangia and antheridia). 



Lyngbye, Hydrophyt. Dan., 1819, p. 130 (in part) ; Bory. in Diet. 

 class, d'hist. nat., vol. 6, 1824, p. 63. Colophermum Rafinesque, Precis 

 decouv. som.. 1814, p. 49. 



