164 Alexander W. Evans, 



16. Riccardia tenerrima (Steph.) comb. nov. 



Aneura tenerrima Steph. Kungl. Svenska Vet.-Akad. Handl. 



49^: g.f.i,i. 191 1. 



Specimens examined : on tree trunks, Puerto Chacabuco, near 

 the mouth of the Rio Aysen, western Patagonia, 1907-1909, Halle 

 5*5 (U., type of Aneura tenerrima) . Known only from the type 

 locaHty. 



The relationship of R. tenerrima to R. autoica is close, and the 

 species is therefore very distinct from any of the others that have 

 been discussed. The plants are dark green, apparently showing 

 very little variation in color, and the thalli, together with their 

 vegetative branches, are prostrate and adherent to the substratum 

 by means of numerous rhizoids. They are sometimes scattered 

 and sometimes crowded together in thin mats. The texture is 

 exceedingly delicate, and it is difficult to dissect off a plant without 

 tearing it. No stolons have been observed. 



The axis (Fig. 8, A) is strongly flattened, the upper surface 

 being plane or nearly so and the lower slightly convex. In well- 

 developed plants the axis is mostly 1-2 cm. long, thus exhibiting 

 long-continued growth, while the width is 1-1.5 mm. and the thick- 

 ness only 0.2-0.25 mm. The thinning out toward the sides is 

 gradual, and an indistinct wing, one to four cells wide and only 

 one cell thick, is usually present. The cross section is therefore 

 acute to acuminate at the ends (Fig. 8, B). In the median por- 

 tion the axis is only five or six cells thick. The surface-cells 

 measure as a rule 60-120 fx in length and about 40 ix in width, while 

 the interior cells are mostly 100-200 x 50 fi. The contrast in width 

 is thus relatively slight. The cell-walls throughout are thin or very 

 slightly and uniformly thickened. 



The branches (Fig. 8, A) are exceedingly variable in length and 

 in degree of subdivision, but are essentially like the axis in their 

 structural features. The primary branches arise at intervals of 

 0.5-1.5 mm. on each side of the main axis and spread obliquely to 

 widely. The longest are about i cm. long and nearly or quite as 

 wide as the axis ; they usually bear a series of simple branches on 

 each side, these being usually 2-3 mm. long and 0.5-1 mm. wide ; but 

 sometimes a secondary branch bears tertiary branches, either vege- 

 tative or sexual in character. The shortest primary branches are 



