CHILEAN SPECIES OF METZGERIA. 



297 



near Puerto Varas, Dusen (20, p. 20) ; Skyring and Dawson Island, 

 Skotisbcrg (24, p. 10); Desolation Island, Dusen (21, p. 10); Ushuaia, 

 Tierra del Fuego, Skotisbcrg (23, p. 9). Also the following stations 

 beyond the boundaries of Chile : New Zealand and Australia, several 

 collectors (19, p. 939); Antipodes Islands (24, p. 10). 



As here understood M. decipiens is probably the commonest and 

 most widely distributed Metzgeria in Chile. It exhibits a great deal 

 of variation in size and particularly in width, in the number and dis- 

 tribution of its hairs and in the measurements of its alar cells. It 

 shows, however, the following apparently constant features; a flat or 

 slightly convex thallus; a costa bounded both dorsally and ventrally 

 by two rows of cortical cells ; a lack of ventral alar hairs ; and a lack of 

 gemmae. Another feature almost as constant is the presence of 

 ventral vegetative branches. It is of course difficult to establish the 

 absolute constancy of any characters in so variable a genus as Metz- 

 geria, especially characters of a negative nature, but the writer has 

 found no exceptions to the four first enumerated after a detailed study 

 of the numerous specimens cited. 



The plants are pale yellowish green and are sometimes scattered 

 but usually form depressed and layered mats of considerable extent. 

 They are frequently found on trees but are by no means restricted to 

 such localities; in rare instances, in fact, they are epiphyllous in habit. 

 The living portion of a thallus is usually 1-2 cm. long, while the width 

 is mostly 0.8-1.2 mm. These figures represent the mean averages 

 obtained from six specimens. The narrowest thallus seen, however, 

 was only 0.2 mm. wide, while the widest was l.S mm. Measured in 

 cells an average wing is usually thirteen to seventeen cells across; a 

 very narrow wing, however, may be as little as two cells and a very 

 wide one as much as twenty-seven cells. The ventral branches are 

 sometimes so abundant that they largely replace the normal branches. 

 When the latter occur to the usual extent the successive dichotomies 

 are mostly 1-3 mm. apart. A ventral branch broadens out abruptly 

 from a narrow stalk-like base and quickly acquires a normal width, 

 often in fact just beyond the margin of the higher axis. Sometimes 

 the branch spreads widely or obliquely; sometimes it grows in the 

 same direction as the higher axis. Under the latter circumstances 

 the axis is usually soon limited in growth; and, if the process is 

 repeated, a more or less definite sympodium may be the result. 



Hairs occur in two positions — along the margin and on the ventral 

 surface of the costa. The marginal hairs (Fig. 6, A) are by far the 

 more numerous and are sometimes very abundantly produced. In 



