The Genus Riccardia in Chile. 135 



continued growth ; it is usually 2-4 cm. long, 0.6-0.8 mm. wide 

 and 0.3-0.35 mm. thick. These measurements signify a certain 

 amount of flattening and the cross section (Fig. 3, A) shows a 

 biconvex outline, more strongly bulging below than above and 

 tapering out gradually on each side to a blunt point. The axis 

 is bounded by narrow and indistinct wings three or four cells thick 

 and covered over both above and below by five or six rows of 

 surface-cells averaging about 30 x 20 11; no row of marginal 

 cells is differentiated. The median portion of the axis is usually 

 twelve to fourteen cells thick, the cells (with the exception of the 

 surface-cells) averaging about 30 /x in diameter. The surface 

 layer and the layer just inside, which is continued into the wings, 

 are composed of relatively thin-walled cells. They are succeeded 

 by one or two layers in which the walls are thickened and often 

 pigmented, but the sclerotic zone thus indicated is far less distinct 

 than in R. Savatieri ; toward the upper surface it is usually clear 

 enough but tends to be indefinite both ventrally and laterally. The 

 interior is made up wholly of cells with pale and scarcely thick- 

 ened walls. With the exception of the wing-cells and the two 

 outermost layers of the median portion, the cells of the axis are 

 more or less elongated. 



At intervals of 1-2 mm. the axis gives rise on each side to 

 obliquely spreading branches, quickly limited in their growth and 

 measuring 2-5 mm. in length by 0.4-0.6 mm. in width. Each pri- 

 mary branch usually bears on each side from one to three secondary 

 branches, the latter being mostly alternate, 0.4-0.8 mm. long and 

 0.2-0.3 mm. wide. When more than one secondary branch is 

 present on a side they are distant and a gradual decrease in length 

 is apparent. The photosynthetic systems thus formed are simpler 

 than in R. Savatieri and other allied species and show a lanceolate 

 or narrowly ovate outline. The secondary branches in their most 

 characteristic development (Fig. 3, B) are more strongly flat- 

 tened than the axis and primary branches, the median portion 

 being only seven or eight cells thick. The wings are about as 

 wide as the median portion and tend to be more clearly defined 

 than in the broader parts of the thallus. They are mostly three 

 cells thick throughout (as described by Stephani) but may be four 

 cells thick next the median portion and only two cells thick toward 

 the edge. At the very edge an interrupted row of marginal cells 



