568 ALEXANDER W. EVANS 



irregular, the primary branches more or less scattered and (if photosynthetic) 

 soon spreading away from the substratum and tending to broaden out into 

 rounded expansions, sparingly subdivided, wings as in the axis, sometimes 

 vaguely crenulate from projecting cells: inflorescence dioicous: cf inflorescences 

 arising singly, spreading to suberect; antheridia mostly four to ten; $ inflores- 

 cence occupying a very short branch, the wing narrow and irregularly crenulate: 

 sporophyte not seen. 



On decayed wood, 300 m.; also on soil. 



Masatierra: Q. Gutierrez, on decayed wood, 300 m. (no. 40), the type- 

 specimen. The author would refer to the same species a sterile specimen from 

 Concepcidn, Chile, collected by R. Thaxter in November, 1905 (no. 6^); this 

 specimen grew on soil. 



The smaller size of R. variabilis, together with its irregular habit (Fig. 3, 

 A — C) will at once distinguish it from any of its predecessors. The plants, 

 however, are not very different in color from R. brevirainosa and R. insularis 

 and show a similar translucent texture. In the more typical individuals, the 

 axis is fairl}' distinct (Fig. 3, C) and is prostrate at the base, the apical portion 

 curving away from the substratum. It is usually 3 — 5 mm. long and at first 

 only 0.1—0.3 mm, wide, but sometimes becomes i — 1.5 mm. broad in the apical 

 portion. The thickness is usually about o.i mm. throughout, thus showing a 

 subterete condition at the base and gradually passing into a strongly flattened 

 condition. In the subterete portion the edges are rounded and wingless; in 

 the flattened portion a row of marginal cells or a wing two or three cells broad 

 is often distinguishable, the wing being subentire or vaguely and irregularly 

 crenulate from projecting cells. In the thickest portion of the axis the cells 

 are in only four or five layers, and the cell-walls are everywhere thin and deli- 

 cate. The surface cells have an average diameter of about 35 [x and are some- 

 times nearly isodiametric especially along the margin; in many cases, however, 

 they are longer than broad and may attain a length of 60 — lOO [i. The interior 

 cells are mostly 120 — 200 [x long and 60 [j. wide, the cross sections thus showing 

 a sharp contrast in size between the cells. 



The branches, which are very irregular and sometimes hardly distinct from 

 the main axis, usually arise at intervals of 0.3 — i mm. At the same time photo- 

 synthetic branches (Fig. 3, D— F) and stolons (Fig. 3, G) can be distinguished, 

 although connected with each other by intermediate types. A typical photo- 

 synthetic branch is narrowed and prostrate at the base and broadens out at 

 the ascending apex into a blunt expansion 0.5— 1.5 mm. wide, thus resembling 

 the apical portion of a main axis. It usually gives rise to a few similar but 

 shorter secondary branches and the latter sometimes bear one or two very short 

 tertiary branches or their rudiments. The cell-structure of the photosynthetic 

 branches is essentially like that of the axis. The stolons are about the same 

 as the basal prostrate portion of the axis or a photosynthetic branch. They 

 are mostly i — 2 mm. broad, simple or very sparingly branched, wingless and 

 but slightly flattened. Their cells average only 20 a in width and show little 

 contrast in cross section between the exterior and interior layers. On the 

 stolons and on the prostrate portions of the other axes rhizoids are abundantly 

 produced; elsewhere they are scanty or absent altogether. 



