The Genus Riccardia in Chile. 119 



relatively many ; toward the outside they are pigmented with brown 

 and strongly thickened, the pits being relatively few. The pig- 

 mented zone is connected by a gradual transition with the pale 

 interior portion ; it is usually from five to eight cells thick and is 

 especially distinct ventrally. The cells outside the pigmented zone 

 are only slightly longer than broad. Those of the superficial layer 

 are the most distinctive, each one projecting as a short and 

 rounded, hyaline, thin-walled papilla. The basal portions of these 

 cells have slightly thicker walls, and the same thing is true of the 

 one or two layers between the surface-layer and the pigmented 

 zone. The surface-layer with its crowded thin-walled papillae 

 extends not only over the axis but over the branches throughout 

 the greater part of their extent. It constitutes one of the most 

 striking peculiarities of the species and gives the whole surface a 

 velvety appearance under the lens. 



At fairly regular intervals of 1-3 cm. the axis gives rise to 

 closely pinnate or bipinnate, obliquely spreading branch-systems 

 (Fig. I, A), broadly ovate in outline and often contiguous. These 

 branch-systems, which are photosynthetic in character, are subop- 

 posite and soon limited in their growth, attaining a length of 5- 10 

 mm. Toward their apices the branches are often decurved, 

 loosely grasping objects with which they are in contact and thus 

 justifying the specific name prehensilis. This feature is well 

 shown in the Flora Antarctica figure (34, pi 160, f.p). The prim- 

 ary branches of these photosynthetic systems are strongly flattened, 

 mostly 0.5-0.7 mm. wide and 0.2-0.3 mm. thick. They are winged 

 throughout, except sometimes in the basal portion, and the wings 

 may even be decurrent for a short distance on the main axis. The 

 ultimate branches (Fig. i, C) are similar to the primary branches 

 but are only 0.25-0.5 mm. in width. Their wings are distinct, each 

 wing occupying about one third the width of the branch. Except 

 at the very edge the wings are three cells thick, the middle layer 

 being composed of short cells with slightly thickened walls and the 

 surface layers, both above and below, showing their character- 

 istic, thin-walled, papillate projections (Fig. i, D, E). In typical 

 cases these extend forward and slightly overlap each other, but 

 they may be too short to do this. The surface-cells average about 

 20 [x in width. At their margins the wings are denticulate or 

 crenulate, being bounded by a single row of hyaline, projecting 



