The Genus Riccardia in Chile. 187 



In R. tenax another species of doubtful relationship presents 

 itself. Here again, in the absence of young plants, the method of 

 attachment to the sul^stratum can not be determined. The speci- 

 mens available are densely tufted, the individual thalli apparently 

 maintaining an erect position, and the plants are unusually stitif and 

 unyielding to pressure. The younger parts of the plants are 

 brownish or yellowish green, but the older parts are much darker 

 and even appear blackish when dry. No rhizoids have been seen. 



The main axis, so far as one can be distinguished (Fig. 12, E), 

 shows a more or less decurved apex and long-continued growth, a 

 length of 1-2 cm. being reached. The width usually varies between 

 0.4 mm. and 0.6 mm., and the thickness between 0.25 mm. and 0.3 

 mm. In the apical portion the flattening is somewhat more pro- 

 nounced than in the basal portion. Both surfaces are somewhat 

 convex, the ventral tending to be a little more so than the dorsal, 

 and there is a gradual thinning ovtt to the edges, which are rounded 

 below and subacute above. The cross section (Fig. 12, G) shows 

 that the axis is nine or ten cells thick in the median portion. The 

 surface-cells average about 35 x 18 ju, and the innermost cells meas- 

 sure 70-120 /x in length by about 35 ^ in width; the increase in 

 size in passing inward is gradual. The second and third layers 

 of cells from the outside have thickened and sometimes pigmented 

 walls. The other cells have thin and either colorless or very pale 

 walls. The margin itself, in the flatter part of the axis, may be 

 bounded by a more or less distinct row of cells, although nothing 

 definite enough to be called a wing is differentiated. 



At intervals of 1-2 mm. on each side of the axis branches or 

 branch-rudiments can be observed (Fig. 12, E). The latter are 

 about as numerous as the branches, and each one shows a blunt 

 lobe arching over the apical cell, which is situated in the angle 

 between the lobe and axis. The tip of the lobe lies under the axis 

 and is visible only from below (Fig. 12, F). Of the vegetative 

 branches which develop three types can be distinguished : leading 

 suberect branches essentially like the axis, flattened branches 

 directed obliquely forward, and subterete branches directed back- 

 ward. The suberect branches are abundantly produced, and 

 Fig. 12, E, shows the difficulty of distingiiishing between the axis 

 and branches of this character. The obliquely spreading branches 

 are soon limited in growth, the best-developed being mostly 



