On American Species of the Genus Potamogeton. 357 



p. 102, e Chamiss. P. exslipulahis, {Muhl) Herb. Willd. part. 

 e Chamiss. 



Hab. Ponds and slow streams ; Cambridge ; and common in 

 New England;, and from the eastern part of New York, {Prof. 

 Torrey!) to western New York, [Prof. Gray!) westward to 

 Kentucky (Dr. Short. Hb. Torr.f) and California, (Chamisso,) 

 sour h ward to South Carolina, {Michaux,) and Louisiana, (Dr. 

 Hale. Hb. Torr. !) Chamisso found it also in the Sandwich 

 Islands. Stem compressed, branched, at first mostly below, but 

 at length very much so above, 6 inches to about l& feet long. 



r 



Leaves membranaceous, dark-green, narrow-linear, above sensibly 

 a little attenuate to the acute and often somewhat mucronate tip, 

 shortly tapering at base and sessile : mostly 3-nerved, but the 

 lateral nerves more or less obsolete and sometimes entirely so ; 

 with commonly but a few scattered veins, but these sometimes 

 frequent and conspicuous, especially in the highest leaves; the 

 space next the midrib on each side more or less widely reticulate- 

 cellulose ; somewhat obsoletely glandulose at base ; 1-2 inches 

 long by £ to i, or, especially in the western plants, f of a line 

 wide. Stipules delicate, short, acute. Peduncles short, com- 

 pressed, thickened immediately below the few-flowered, capitate, 

 ' sub-globose spike, which is more or less reversed in flower but 



( becomes erectish in fruit. Nutlets compressed, subtricarinate ; 



the back a little curved downward below the apparent base, and 

 sinuate-dentate ; either acutely subalate-carinate, when the whole 

 outline is obliquely elliptical, or semicircular and broad-alate, 

 when the outline is rounded-obovate ; mucronate-rostrate with 

 the short style ; the lateral keels obsolete ; the sides very slightly 

 convex, and until quite mature, punctiform-im pressed at the mid- 

 dle: the face acutish, or in the broad-winced fruits, carinate. 

 Exocarp rather thin; produced at the back and forming the wing. 

 Putamen thick, not hard. Seed convolute-uncinate. The exo- 

 carp bein<* removed the back appears more or less acvU/y cari- 

 nate. The stress of difference between this species and P. pu- 

 stilus, (?, is in the fruit : though the darker color of its more con- 

 stantly acute, and more venose leaves, its shorter stipules, and its 

 short-peduncled, few-flowered, subglobose spikes, will also fur- 

 nish perhaps quite reliable diiferences. And I have thus far found 

 the commonly conspicuous glands at the base of the leaves of 

 P.pusilliis. a safe index to that species; these glands in the 

 present, so far as my observation has gone, being either nearly or 

 quite obsolete ; as Kunth, who inserts ' eg/nndulosis? 7 into his 

 character, appears to have found them. The discrepancy be- 

 tween the descriptions of the fruit given by Chnmisso and by 

 I Kunth seems to be reconciled by a consideration of the varying 



j width of the wim this difference serving to alter materially the 



whole outline of the nutlets. In the very narrowly winged fruits, 



