122 Rhodom [June 



pectinatus L., P. filiform is Pers., and their allies, forming the section 

 Colcophylli, and venture to make known my conclusions as to the 

 North American species. The section Coleophylli Koch is character- 

 ized by the possession of submersed leaves only, which are adnate for 

 some distance at the base with the stipule, forming a clasping sheath. 

 The members of the group as now understood can be distinguished 

 by means of the following key. 



A simple notation is used to indicate the collections in which the 

 specimens cited may be found. 



(A) Academy of Natural Sciences of Philadelphia. 



(C) Canadian Geological Survey. 



(H) Gray Herbarium. 



(N) New England Botanical Club. 



(R) Rocky Mountain Herbarium. 



(Y) Eaton Herbarium, Yale University. 



A. Leaves auriclcd at base, stiffly two-ranked, with a cartilaginous, finely 



and sharply serrate margin 1. P. Itobbinsii Oakes. 



A'. Leaves not auricled at base, not definitely two-ranked, not serrate. 

 B. Style slender, incurved, persistent as a beak on the mature fruit. 

 C. Leaves (except those of the first year's shoot which arc coarser and 

 blunt) 0.2-1 mm. broad, acute, taper-pointed; sheaths but slightly 



thicker than the stem 2. P. pectinatus L. 



C. Leaves 2-4 mm. broad, obtuse or shortly apiculate; the upper short, 

 1.5-2.5 cm. long; sheaths loose, 2-4 times thicker than the stem. 



3. P. latifolius (Robbins) Morong. 

 B'. Style wanting, fruit beakless; leaves retuse, blunt, or often shortly 

 apiculate. 



D. Whorls of flowers 5-12, evenly spaced, or the lower somewhat 

 more remote: the upper leaves filiform; primary sheaths swollen, 

 2-5 times thicker than the stem, bearing short ribbon-like blades. 



4. P. moniliformis St. John. 



D'. Whorls of flowers 2-5, the upper approximate: sheaths tight, all 



bearing filiform blades. 



E. Mature spike elongate, moniliform, 1.5-5 cm. long; verticels 



mostly remote, the upper 3-12 mm. apart, the lower usually 



0.7-2.5 cm. apart 5. P. fdiformis Pers. 



E'. Mature spike short, 0.5-2.5 cm. long; the upper verticels 

 mostly approximate, the lower approximate or at most 7 mm. 

 apart. 

 F. Leaves fine, 0.25-0.5 mm. broad, retuse or obtuse. 



5a. P. fdiformis Pers., var. borealis (Raf.) St. John. 



F'. Leaves coarse, 0.75-2 mm. broad, obtuse or shortly apiculate. 



5b. P. fdiformis Pers., var. Macounii Morong. 



