172 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



Branch leaves when dry not 5 ranked. 



Branch leaves with isolated pores on inner face toward apex. 

 Hyaline cells of stem leaves mostly with fibrils, branch leaves not 



shining. 



Stem leaves extended into a blunt point with invo- 

 lute margins . . . . . . g. tenerum, 8. 



Stem leaves scarcely pointed, not involute S. acutifolium, 13. 



Hyaline cells of stem leaves mostly with fibrils, branch 



leaves silky shining S. su buttons, 9. 



Branch leaves with numerous pores upon entire inner 



face S. microphyllum, 10. 



B. Branch leaves toothed at apex and upper margins; border with 

 resorption-furrows. 



Stem leaves small (1.14-1.28 mm.), narrow border plainly 



broadened near the base . . . . S. Labradorense, 11. 



Stem leaves larger (2-2.10 mm.), narrow border scarcely 



broader at the base S. molle, 1 18. 



II. Squarrosa. 



Dioicous, perigonial leaves scarcely different from the 



leaves of the sterile branches S. teres, 16. 



Monoicous, perigonial leaves smaller, curved, erect 



spreading S. squarrosum, 16. 



III. Cuspidata. 



A. Branch leaves without fibrils. 

 Pits on the outer surface large (10-12/* diam.), 5-16 in a 



single row in the middle of cell . . . S. macrophyllum, 24. 

 Pits on the outer surface smaller (4-5/* diam.), 40-60 in 



each hyaline cell . ' S. Florid anum, 12. 



B. Branch leaves always with fibrils. 



i. Branch leaves ovate-lanceolate or lanceolate to almost long 



linear. 



a. Stem leaves lacerate-fimbriate in the upper part. 



Stem leaves widened upward, spatulate, fringed at apex S. Lindbergii, 15. 

 Stem leaves triangular linguiform, lacerate two-cleft at 



the apex . ... . . . S. riparium, 13. 



i Including S. Muelleri Sch., L. & J. Man. 17. 



