378 University of California Publications in Botany [Vol. 7 



Myrioncma such as M. phyllophyhim S. and G. They, in part, possess 

 unisori;itc loculi. Imt have many perpendicular and slanting walls, 

 iii;il<ing a partial biseriate condition. The basal layer, particularly in 

 the center of the thallus, is distinctly distromatic, developing numerous 

 peg-like rhizoids, which serve to anchor it more firmly to the host, and, 

 for the most part at least, the branching of the filaments is subterminal, 

 whereas that of a true Myrionema is terminal and brought about by 

 the splitting of the apical cell. 



The size of the plants as a whole varies considerably. The material 

 of the type varies in this respect from 4 mm. to 7 mm. in diameter. 

 In some collections of specimens which we have included under the 

 species, the specimens are as small as 2 mm. in diameter, in others they 

 are up to 10 mm. in diameter. The length of the erect filaments 

 varies from 150/x. to 500/*. JMature gametangia vary from 55/* to 120/a 

 long. The relative number of gametangia terminal on the erect fila- 

 ments, as well as their size and complexity, is exceedingly variable in 

 different collections. Two or three cells only may metamorphose in 

 some filaments, in others eight or ten. Occasionally small lateral out- 

 growths from these metamorphosed cells may occur. The number of 

 erect filaments in proportion to the number of gametangia is a char- 

 acter which seems to be very unstable. In some collections they exceed 

 the number of gametangia almost two to one, in others they do not 

 occur more than in proportion of one to five. Tliej' are very irregular 

 in origin along the radiating creeping filaments. Some near the 

 margin of the frond may be nearing maturity before others near the 

 frond have started (pi. 41, fig. 5). 



Hecatonema clavatum sp. nov. 



Plate 40, figures 1-4 



Frondibus pulvinulos orbiculares, 2-3 mm. diam., margine lato 

 filamentis ereetis destituta formantibus; parte prostrata per rnmnlos 

 radii-iformes nunierosos. breves, subulatosque adhaerente. et filamentis 

 regulariter radiantibus, dense compactis composita ; filamentis ereetis 

 plerumque clavatis simplieibus, 190-210;u, longis; cellulis filamentorum 

 repentium 5-6^ diam.. 1.5-2-plo longioribus; cellulis filameiiloi'um 

 erectorum inferne eylindrici.s. 5.5-6.5/* diam., 2-2.5-plo longioribus. 

 superne ad discepimenta leviter constrietis, 8-11/* diam., 1.5-plo 

 longioribus; zoosporangiis( ?) in filamentis repentibus. sessilibus sub- 

 sessilibnsve, clavatis, 60-80/* longis, 10-14/* latis; gametangiis cylin- 

 dricis us(|ue ad leviter fusiformibus. in filamentis repentibus .sessilibus 

 brevi-pedicellatisve, 55-85/* (usque ad 110/*) longis, 8-12/* latis; loculis 

 plerumque 2-seriatis. 



