THE THALLOSli HEI'ATICAK OF THE JUAN FERNANDEZ ISLANDS 573 



MetzfAcria RaHdi. 



*I4. M. decrescens Stepli. Hull. Herb. Boissicr 7: 932 (1899); I'^vans, I'loc. 

 Am. Acad. 58: 279 f. 2 (1923). 



On rocks in ravines and in beds of streams, 1000 m. and above. 



Masafucra: along a brook, looo m., Skottsherg 1908 (no. 29, cited by 

 Stkpiiani, p. 10, as I\f. cJiilensis Steph.); ravine near the Campo Correspondencia, 

 1 1 50 m. (nos. 44, 45); the High Plateau, iioo m. (no. 46). 



The specimens here referred to M. decrescens are by no means typical, 

 and some of them diverge rather strikingly from the Chilean material recently 

 reported upon by the writer. These divergent specimens, however, are con- 

 nected by insensible intergradations with less aberrant forms, and the latter 

 could hardly be distinguished from some of the less robust Chilean plants. 

 There seems to be no reason, therefore, for attempting to separate the Juan 

 Fernandez specimens specifically. 



The two plants that approach typical J/, decrescens most closely are no. 

 44 from the vicinity of the Correspondencia Camp and the plant from the 

 1908 collection, determined as J/, chilensis by Stephani. In these the thalli 

 are distinctly convex, as they should be, the marginal hairs are borne singly, 

 and the thallus is otherwise naked, except for a few scattered hairs on the 

 ventral surface of the costa. Ventral vegetative branches, however, are occa- 

 sionally present, and the costae are relatively simple, the rows of cortical cells 

 rarely exceeding four either dorsally or ventrally. Although no ventral branches 

 except those with sexual organs have as yet been demonstrated in the Chilean 

 material, it would be unwise to state definitely that they are constantly absent; 

 and costae as simple as those of the Juan Fernandez plants .are often to be 

 found on poorly developed thalli or on some of the branches of robust thalli. 



No. 45 from the vicinity of the Correspondencia camp and the specimen 

 from the High Plateau dift'er in two more important respects, many of the thalli 

 being plane or nearly so and the ventral surface of the costa often bearing 

 densely crowded hairs. Even here, however, a few branches are distinctly con- 

 vex and parts of the costae are nearly or quite free from hairs. On the whole 

 the plants with plane thalli present the appearance of being poorly developed, 

 and yet their costae often approach in complexity those of robust Chilean 

 specimens. It should be added that the Juan F'ernandez plants often show the 

 gradual transition between the unistratose wings and the costa, so characteristic 

 of M. decrescens. 



When the writer discussed this species on the basis of the Chilean ma- 

 terial no female branches were found except a few too badly disintegrated to 

 be described. No. 45, cited above, shows female branches in considerable 

 abundance. They are more or less strongly concave and show the usual ob- 

 cordate outline, although the apical sinus is sometimes very shallow. Their 

 length is mostly 0.45 — 0.5 mm. and their width 0.5—0.6 mm. The marginal 

 hairs, which are borne singly, are sometimes separated by one or two cells, but 

 often a series of hairs will adjoin one another, each representing the projection 



