13° Alexander W. Evans, 



are strongly flattened and show distinct wings three or four cells 

 wide and one cell thick (Fig. 2, G, H). The median portion is 

 about as wide as the wings and four or five cells thick. The 

 interior cells are elongated and thick-walled, forming a narrow 

 band or strand ; the surface-cells of the median portion are short, 

 mostly 25 jx wide, and scarcely show trigones. The cells of the 

 wings are slightly wider but gradually decrease in width toward 

 the margin, the cells next to the median portion measuring about 

 40 /x in width, those of the second row 37 /x, those of the third row 

 34 IX, and those of the marginal row 20-30 fx. The wing-cells have 

 distinct trigones, and scattered cells along the margin sometimes 

 project as blunt or subacute teeth. Between the ultimate branches 

 and the flattened main axis are all possible gradations. The 

 stolons (Fig. 2, F) show a structure which is essentially like that 

 of the prostrate axis, except that the zone of thick- walled elongated 

 cells is very indistinctly defined. 



The male plants observed (see Fig. 2, B) are rather more slender 

 than the female, but it is doubtful if this difference is at all con- 

 stant. The male branches arise in the basal portion of a photosyn- 

 thetic branch-system, sometimes representing primary branches 

 and sometimes secondary branches of one of the lowest photosyn- 

 thetic branches. In some cases a male branch is tipped immediately 

 by an inflorescence, but it usually subdivides almost at once into 

 from two to eight branches, each tipped by an inflorescence, the 

 whole forming a divaricate cluster. The individual inflorescences, 

 which apparently never proliferate, are mostly 0.6-0.9 mm. long 

 and 03.-0.35 mm. wide. The antheridia are mostly six to ten in 

 number, and the openings into the antheridial chambers are usually 

 separated by two rows of cells. The narrow marginal wing, 

 usually two cells wide, spreads slightly and is vaguely and irregu- 

 larly crenulate from projecting cells. 



The female branches (Fig. 2, A), rarely as many as four on a 

 thallus, are borne in the lower part of a photosynthetic branch- 

 system and represent either primary branches or the basal branches 

 of secondary branches, agreeing in these respects with the male 

 branches. The inflorescence is borne close to the base of the 

 branch, which usually continues its growth beyond the archegonia, 

 sometimes forming a simple strap-shaped extension but usually 

 giving rise to secondary or even tertiary branches, very much as 



