158 Alexander IV. Evans, 



resembles the majority of the branches. The upper surface of the 

 axis is sHghtly convex and is covered over by a single layer of large 

 cells (Fig. 6, B, C) ; the lower surface is more convex and the 

 edges are rounded to obtuse. The large cells of the upper surface 

 are mostly 80-160 /x long in the median portion and 60-80 /x wide; 

 toward the edges they gradually become shorter, the marginal cells 

 averaging about 50 /x in length and forming a more or less distinct 

 border. The cells of the lower surface are almost as long as those 

 of the upper surface but distinctly narrower, being only 30-50 /x 

 wide. The interior cells measure 1 60-200 /x in length and average 

 about 40 jx in diameter. In cross section the large cells of the upper 

 surface stand in rather sharp contrast to the other cells and repre- 

 sent an unusual feature for the genus. The axis is usually four to 

 six cells thick, and the cells are thin-walled throughout. 



The axis gives off, usually at intervals of 0.6-0.9 ^^- o^'' ^'^^^^ side, 

 a series of obliquely spreading branches. A few of these represent 

 new axes and branch in the same way as the main axis, but the 

 majority are shorter and narrower and usually grow out into 

 attenuate apices. These shorter primary branches usually give ofif 

 a few simple secondary branches, these being still narrower and 

 almost invariably attenuate. A few of the branches arising in the 

 basal part of the thallus represent stolons ; these are slender and 

 usually simple, their width being mostly 0.1-0.12 mm. The ordi- 

 nary branches show much the same structure as the main axis. 

 The more slender examples are only four cells across on the upper 

 surface and four cells thick in the median portion. The row of 

 marginal cells is usually very distinct and the cells sometimes 

 project as crenulations. The stolons (Fig. 6. D) are only slightly 

 flattened and do not show a marginal row of cells ; they are about 

 five cells thick and their small cells, which average only 20 /x in 

 width, show little differentiation. 



The male branches, which are simple and apparently never 

 proliferate, arise directly from the main axis or from an axial 

 branch (Fig. 6, A). The inflorescence (Fig. 6, E) occupies 

 nearly the whole of the branch and is usually 0.45-0.7 mm. long and 

 0.3 mm. wide. The wing, which is a single cell wide, is either sub- 

 erect or obliquely spreading and its cells project as distinct crenu- 

 lations. The antheridia vary in number from six to ten, and the 

 openings into the chambers are commonly separated by single 

 rows of cells. Sometimes these cells bulge upward, the upper 



