The Genus Riccardia in Chile. 195 



lowish or brownish when dry, and grow in depressed mats in 

 admixture with other bryophytes. Rhizoids are absent from the 

 greater part of the thallus, but in the isolated areas where they 

 occur they are fairly abundant, their development apparently being 

 a response to contact with the substratum. 



The axis, so far as one can be distinguished, is at first prostrate 

 and shows long-continued growth (Fig. 13, I). Eventually, 

 however, it turns upward and its growth is brought to an end. The 

 living portion is mostly 0.5-1 cm, long, 0.5-1 mm. wide and 0.15-0.2 

 mm. thick. From the thickened median region, which is eight to 

 ten cells from top to bottom, it gradually thins out toward the 

 rounded margins, which show neither wings nor modified rows of 

 cells. The marginal portions are more or less involute so that the 

 thallus appears crescentic in cross section, the dorsal surface being 

 concave and the ventral convex. The thallus in addition is irregu- 

 larly sinuate and crispate along the margin. The cells on the 

 upper surface are about 30 [x long and 23 jx wide, but on the lower 

 surface they have an average width of only 15 /x. From these 

 small surface-cells toward the interior a gradual increase in size 

 is apparent, the internal cells being mostly 80-140 /x long and 30- 

 40 /x wide (Fig. 13, J). The outer walls of the ventral surface- 

 cells are slightly thickened ; otherwise the v/alls are exceedingly 

 thin and delicate. 



The branching is very irregular, the branches sometimes being 

 as much as 3 mm. apart and sometimes very closely crowded. 

 Most of them spread obliquely and are essentially like the axis. 

 When they are crowded they give rise, with their irregularly sinuate 

 and crispate margins, to intricate clusters in which it is difficult to 

 distinguish the component parts. Not infrequently the margins 

 shows thickened regions, representing the growing points of new 

 branches, and these make the clusters appear still more com- 

 plicated. An occasional branch is subterete and stolon-like, con- 

 sisting of little more than the thickened median portion, but such 

 a branch retains the power of broadening out into a branch of the 

 usual type. 



Only a few male branches have been observed by the writer and 

 these were not wholly satisfactory for study. They are narrower 

 than ordinary branches, measuring about 0.3 mm. in width and bear 

 a strong resemblance to the stolon-like branches, the thin marginal 



