2l6 GEOLOGICAL SURVEY OF CANADA, 



stereid band ; the first of these also has the leaves smooth or 

 papillose and the second has a leaf lamina of two layers of cells, 

 mamillose on the upper surface only. 



This genus is dedicated to Mrs. Elizabeth G. Britton, by whose 

 aid so many American students of our mosses have been en- 

 couraged. 



1003. B. pellucida, R. S. Williams. 



With much the habit of Tortula laiifolia but leaves much longer 

 and narrower above. Stems mostly simple, radiculose below, in 

 loose, rather dark green tufts up to 2 cm. high, in cross-section 

 irregularly oval (about .320 mm. long) with walls of two or three 

 rows of slightly thickened irregular cells, ground tissue of large 

 thin-walled cells, surrounding a distinct central strand of numer- 

 ous small thin-walled cells. Terminal leaves (often enclosing 

 numerous long paraphyses-like hairs) oblong-lanceolate, up to 

 7.5 mm. long and 1.5 mm. broad, plicate and somewhat crispate 

 when dry or rarely nearly straight, mamillose on both faces 

 except dorsal side of costa, crenulate-serrate on flat borders in 

 upper half, obtusely or somewhat acutely pointed, with stout 

 costa (.140 mm. wide near base) long-decurrent on stems and 

 vanishing several cells below apex. Lower leaves ovate-oblong 

 (about 3 mm. long). Leaf cells above rhomboidal to hexagonal, 

 about .016 mm. in diameter, becoming gradually elongated below 

 and hyaline, the cells near margin a little above base .004 — .006 

 mm. wide and up to .160 mm. long, toward costa .020 — .025 mm. 

 wide and up to .100 mm. or more long. Cross-sections of costa 

 show in the ventral half about 4 guide-cells with a few accessory 

 cells or even i or 2 rows of accessory cells nearly as large, in 

 addition to the row of mamillose cells on ventral surface. The 

 dorsal half of costa consists of a stereid band, the outer row of 

 cells a little larger than the others with a distinct central strand 

 of small, irregular, thin-walled cells. 



Yukon River bluff, just below Dawson, Yukon, April i6th, 

 1899. {Williams^ 



43. SCOULERIA, Hook. 



In an article by Mrs. E. G. Brit! on in Vol. XXIV., pp. 36-43 

 of the Torrey Bulletin the reader will find the three species given 

 on pages 61-62 of part VI. of my Catalogue of Canadian Plants 



