The Genus Riccardia in Chile. 169 



monly 1-2 cm. and 1-1.5 mm. wide (Fig. 8, C, and Fig. 9, A). 

 In some cases it shows a tendency to Ijroaden out gradually toward 

 the apex, especially if the basal portion is narrow. It is strongly 

 flattened, being plane or nearly so above, slightly convex below, 

 and thinning out gradually toward the margins, where a single row 

 of cells can be distinguished or, more rarely, two rows. The 

 median portion is only 0.2-0.25 mm. thick, representing five or six 

 layers of cells (Fig. 9, B). The surface-cells here average about 

 60 /x in length by 30 /x in width ; toward the margin they gradually 

 become larger, the cells of the marginal row being often 80-100 /x 

 long and 40-50 ix wide. The interior cells are about 50 ju, in width 

 and 160-280 jx in length. There is thus a rather marked contrast 

 in size between the surface-cells and the interior cells of the median 

 portion when these are examined in cross section. The cell walls 

 throughout are slightly but distinctly thickened, the thickening 

 being especially marked in the marginal and superficial cells. 



The primary branches (Fig. 8, C, and Fig. 9, A) show a ten- 

 dency to be opposite and arise at intervals of 0.7-1 mm. on each 

 side of the axis. The branches spread obliquely and often 

 broaden out toward the apex. An occasional branch represents 

 a new axis but the majority are quickly limited in growth. 

 Branches of this character are mostly 3-5 mm. long and 0.5-1 mm. 

 wide. The primary branches usually give rise to a very few secon- 

 dary branches, which are 0.6-1.2 mm. long and 0.4-0.6 mm. wide. 

 In some cases these secondary branches do not develop but remain 

 as short and perhaps latent rudiments. Such a rudiment may be 

 indented at the tip, with the apical cell in the indentation, or the 

 apical cell may be in an indentation between the rudiment and the 

 primary branch. Under these circumstances the rudiment looks 

 like a short rounded lobe. Stolons are indefinite in position and 

 only slightly differentiated, never approaching a terete condition. 

 In their histological structure the branches are essentially like the 

 main axis, except that they are slightly thinner and more fre- 

 quently bordered by two rows of cells (Fig. 9, C, D). 



The sexual branches are very short and arise either from the 

 axis itself or from the base of a primary branch. In the latter 

 case there are usually only one or two on each side. The follow- 

 ing four types of inflorescence occur in the species, all four being 

 sometimes present on an individual thallus (Fig. 8, C) : male, 



