("3) 



Aug. 27, also sterile specimens on dry rock at Lakes Linde- 

 man and Lebarge (563). 



Pottia latifolia pilifcra (Brid.) Muell. On bare earth of 

 river bluff just below Dawson (564). 



Didymodon rubellus (Hoffm.) B. & S. Canon City, Dyea 

 Creek, also common at Dawson. The apex of the leaf of this 

 species usually terminates in a somewhat enlarged, pale, 

 smooth cell with one or two similar cells on either side, form- 

 ing teeth that stand out very distinctly from the rest of the 

 rather obscure papillose cells of upper leaf. The capsule 

 varies greatly in length and breadth. Cells of the lid not in 

 oblique rows (565). 



Ditrichum giganteum R. S. Williams, sp. nov. 



Dioicous. Growing in large cushions up to 12 cm. high, 

 usually of a yellow-green color. Upper stem leaves up to 

 7 mm. long, narrowly subulate above, sharply denticulate at 

 apex and more or less serrulate or crenulate on border about 

 ^ down, also often rough on back above. Inner perichaetial 

 leaf truncately narrowed to a denticulate subula about equal- 

 ing the broad part in length. Cell walls thickened through- 

 out except in and near margin at base. Cells in upper leaf 

 3-5 times longer than wide with rounded ends, in middle 

 near margin, short and irregular, often not or scarcely elon- 

 * gated, toward base several rows in margin narrowly rectan- 

 gular, 8-10 times longer than wide, with thin walls, within 

 the cells become much wider, thick-walled and near costa, 

 mostly pitted. Capsule oblong-cylindrical, not quite sym- 

 metrical, with conical lid ^ its length and broad annulus of 

 3 rows of cells. Three or 4 rows of elongated cells about 

 mouth of capsule, below the cells becoming irregularly ob- 

 long to rectangular, mostly 2-4 times longer than wide. 

 Teeth pale, very papillose, rather broad and irregular, with- 

 out distinct articulations. (Plate 15.) 



This plant is closely related to jlcxicaulc with which it has 

 been associated both in this country and Europe, and some of 

 the larger forms of jlcxicaule approach it very closely but I 

 have not yet seen any with such long, slender, serrulate 

 leaves with inner perichaetial leaf truncately narrowed to so 

 dentate a subula. The color and size alone are usually 



