THE THALLOSE HEPATICAE OV THE JUAN FERNANDEZ ISLANDS 57 I 



both with limited growth (Fig. 4, A — C). The axis itself, however, in many 

 cases if not always, curves away from the substratum after a while and has 

 its own growth brought to an end, and branches of a character intermediate 

 between the extreme types are of frequent occurrence. In consequence of the 

 ascending branches the plants form velvety mats, although the texture is too 

 delicate to give them much rigidity. The color and degree of translucency are 

 much as in R. variabilis. 



The prostrate axis (Fig. 4, U) is mostly 2 — 4 mm. long, 0.2—0.4 mm. wide 

 and 0.15 mm. thick in the middle. It is therefore more or less distinctly flat- 

 tened but usually turns an edge rather than a surface to the substratum. From 

 the median portion, where the cells are in four or five layers, it thins out rather 

 abruptly and is usually bounded on one or both sides by a unistratose wing 

 one or two cells wide. The surface cells average about 55 X 40 (x, becoming 

 shorter toward the edges, the marginal cells being only about 35 (j- long. The 

 interior cells average 60 [x in width and are usually 120— 140 [i long; the cross 

 section thus shows a contrast in size, although this is less marked than in some 

 of the preceding species. The cell-walls are thin and delicate. 



The photosynthetic branches in most cases arise from one edge of the 

 axis and the stolons from the other, but stolons are occasionally borne on the 

 photosynthetic branches in the basal part. The branches are sometimes so 

 close together that they almost touch and sometimes as much as i mm. apart. 

 The photosynthetic branches, when normally developed, are 1.5 — 3 mm. long, 

 0.3 — 0.6 mm. wide, and a little thinner than the axis. Their sides tend to be 

 parallel and their apices are truncate or slightly emarginate. In many cases 

 these branches are simple; in other cases they show a very few secondary 

 branches, which are nearly as wide but usually much shorter. From the median 

 region, which is only four cells thick, the branches gradually thin out toward 

 the edges, where crenulate wings two or three cells wide are commonly devel- 

 oped. The cell-structure is essentially the same as that of the axis (Fig. 4, E). 

 The stolons are sometimes simple but often more or less branched, occasionally 

 forming coralloid branch-systems. They are usually O.i mm. or less in width 

 and show much the same structure as the stolons of R. variabilis, the edges 

 being windless and the contrast in width between the external and internal cells 

 being slight. Rhizoids are fairly abundant on the stolons and other prostrate 

 axes but are rare or absent elsewhere. 



The male and female branches are borne on distinct individuals. The 

 male branches arise singly, usually from the prostrate axis (Fig. 4, B), more 

 rarely from the base of an ascending branch (Fig. 4, C), still more rarely from 

 a stolon. In most cases the inflorescence occupies the whole or the greater 

 part of the branch, but occasionally a short flat proliferation is developed. 

 The inflorescence is large, when the size of the plant is taken into account, 

 the length being 0.7—1.5 mm. and the width 0.25-0.35 mm. The structure, 

 however, is remarkably simple (F^ig. 4, F"), the openings into the antheridial 

 chambers being separated by a single row of cells. The antheridia are mostly 

 ten to twenty, and the crenulate, erect or incurved wing, one cell high, scarcely 

 bulges above the general surface. 



The female branch is borne on the prostrate axis or at the base of a 



