316 EVANS. 



Islands. In Asia it occurs abundantly in the Himalayas and is found 

 also in Japan, Java and Sumatra. In America its northernmost 

 station, so far as known, is in Alaska. It reappears in the Allegheny 

 Mountains, although rarely collected there, and seems to attain its 

 most vigorous development in Jamaica and other West Indian islands. 

 Although not yet known from Mexico it occurs in Guatemala and 

 Costa Rica and has been reported in South America from British 

 Guiana and Brazil and along the chain of the Andes from Colombia 

 to Bolivia. In Chile, as noted above, its range extends far into 

 antarctic regions. It has been cited also from New Guinea and New 

 Zealand. 



The following characters of M. hamata, emphasized by Lindberg in 

 his descriptions, are perhaps the most important: the dioicous inflores- 

 cence; the convex to subterete thallus with re volute wings; the 

 crowded marginal hairs, usually arising in pairs; the wings otherwise 

 destitute of hairs; the costa bounded both dorsally and ventrally by 

 two rows of cortical cells and bearing hairs on its ventral surface. 

 These characters, in spite of the wide distribution of the species, are 

 found with remarkable constancy. There is, to be sure, a considerable 

 range of variation in the convexity of the thallus and in the abundance 

 of the hairs, especially those of the costa, but this would naturally be 

 expected. When the hairs are considered in more detail they are 

 found to vary in certain of their features. In the more typical plants 

 the hairs of a marginal pair diverge widely and are more or less strongly 

 curved, the concavities of the curves being directed downward or away 

 from the edge of the wing. In subterete thalli a fairly dense weft of 

 hairs may thus be formed, partially concealing the costa. This 

 typical condition, however, is by no means constant; in many thalli 

 the hairs are either straight or irregularly curved, or contorted and 

 extend in various directions (Fig. 10, A-E). When the hairs are spar- 

 ingly developed, some of them may arise singly; when they are un- 

 usually crowded, some of them may be in three's or four's (Fig. 10, E). 



The cells of the wings have delicate walls, sometimes with minute 

 and inconspicuous trigones, and vary a good deal in size. It is not 

 unusual, in fact, for the cells in one part of a thallus to be considerably 

 larger than those in other parts, just as in M. decipiens and other 

 species. According to the writer's measurements 50 X 37 n would 

 express the average size of the cells, although Stephani's figures, 65 X 

 50 fx, and Lindberg's, 50-65 lx, are both a little higher. 



According to Lindberg the male branches, which seem to be rarely 

 present, are smooth on the wings and bear a very few short hairs on 



