[295] HEPATIC^E OF ALASKA 349 



Gymnomitrium obtusum is probably as common in the northern parts 

 of North America as in northern Europe, but is known with certainty 

 from very few localities. So far it has been recorded from Greenland 

 only, where it was collected many years ago by Vahl. It has, how- 

 ever, been found by Holzinger in northwestern Montana and by J. 

 Macoun on Vancouver Island. The specimens of the latter were dis- 

 tributed as Cesia concinnata, in * Canadian Hepaticae,' no. 63. 



Although Gymnomitrium obtusum is the only member of the genus 

 occurring in the Harriman collections, two other species have been 

 reported from Alaska: G. concinnatum (Lightf.) Corda, which was 

 collected at ' Tahiti ' by the Drs. Krause, and G. coralloides Nees, 

 which the same collectors found in the ' Dejathal.' The latter species 

 has also been found on St. Paul Island by Merriam and by J. M. 

 Macoun. G. coralloides is rather closely related to G. obtusum, but 

 can readily be distinguished even in sterile condition. In G. coral- 

 loides, the very young leaves are shortly but distinctly bilobed at the 

 apex with rounded or obtuse lobes and narrow sinus. On the margin 

 is a single row of thin-walled projecting cells, making the leaf dis- 

 tinctly crenulate, at least in the upper part. As the leaf becomes 

 older, the walls of these marginal cells remain thin, except where they 

 bound the next inner cells; the cells themselves become perfectly 

 hyaline and lifeless, the projecting outer walls collapse and are some- 

 times entirely worn away, so that the outlines of the cells become 

 very indistinct. On account of these changes, the shallow sinus of 

 the leaves grows less and less marked, and in mature leaves cannot 

 always be distinguished. The cells just within the empty marginal 

 cells acquire thick walls very early. The thickenings first appear as 

 small but distinct trigones; these increase in size very rapidly and 

 soon become confluent, so that the cell-cavities are oval or circular in 

 outline. Several rows of these cells also become empty and hyaline, 

 but their thick walls prevent them from collapsing. The green cells, 

 which are found in the middle and toward the base of the leaf, have 

 thin walls and small, sometimes very minute, trigones. They pass 

 by gradations into the thick-walled submarginal cells. The cuticle of 

 the leaves is smooth throughout. 



10. Marsupella emarginata (Ehrh.) Dumort. 



Port Wells (T. 2273) ; Columbia Fiord (C. & K. 1383, in part, 

 13840, 1386); Juneau (Setchell 1232). New to Alaska. 



The closely related Marsupella sphacelata (Gieseke) Dumort. has 

 already been collected in Alaska by the Drs. Krause. 



