298 NAIADACE.E. Potamogeton. 



very acute and mucronate, narroAved to the eubpetiolate base : otherwise like the 

 last, of Avhich it is scarcely more than a variety. — Amer. Journ. Sci. 2 ser. vii. 354. 

 Walker's Basin {Rothrock, n. 292) ; in the Atlantic States, from the Great Lakes to South Caro- 

 lina, but not common. 



1 3. P. pusillus, Linn. Stem filiform, branching : leaves narrowly linear, 1 or 2 

 inches long, rarely a line wide, often nearly setaceous, 1-5-nerved, obtuse and 

 mucronate or acute, biglandular at base and sessile ; stipules obtuse, becoming setose : 

 spikes capitate, or somewliat elongated and open, or interrupted, on slender flattened 

 petluncles |- to nearly 2 inches long : fruit as in the preceding, but more obscurely 

 and obtusely keeled : embryo less incurved. — Eeichenb. 1. c, t. 22. P. trichoides, 

 Benth. PI. Hartw. 341. 



In pools and ditches ; near Santa Cruz {Hartweg, n. 2016) and at Soda Springs on the Upper 

 Tuolumne (Bolandcr), the form with subsetaceous acute or cuspidate leaves, distinguished as var. 

 tcnuijisimus, Mert. & Koch. The typical European form occurs in the northern Atlantic States 

 and in British America. 



-f- -f- Stipules united with the sheathing base of the leaf: sjAkes interrupted. 



14. P. pectinatUS, Linn. Stem filiform, repeatedly branched: leaves very 

 narrowly linear, 2 to 6 inches long, rarely over half a line broad, often setaceous, 

 l-nerved, acute : peduncles elongated, slender : spikes | to 2 inches long : fruit in 

 often dense verticils, large (2 lines long), obliquely obovate, compressed, obtusely 

 keeled, acute: nutlet very thick: embryo spirally incurved. — Eeichenb. 1. c. 11, 

 t. 19. 



Yar. (?) latifolius, Eobbins. Stem stouter: leaves short and broader (1 or 2 

 inches long by a line or two broad), 3 - 5-nerved with numerous transverse veinlets, 

 acute or obtuse : sheaths large, with scarious margins, exceeding the obtuse scarious 

 stipules. — Bot. King Exp. 338. 



In various parts of California [Chamisso, Coulter, Douglas) ; Santa Barbara (.1/;-s. Ehvood Cooper); 

 Oregon and Washington Territory {Lijall, Hall) ; Northern Nevada and Utah ( //V/Asch), and com- 

 mon in the Atlantic States as well as in Europe. The variety has been oollirtid iu King's liiver 

 and at GuUing's Hot Spring, Lassen County {Lcmmoii), and in the lower Hunilwldt Kiver 

 ( Wcdson) ; it appears to scarcely differ from the European marine species P. zosteraceus, Fries, to 

 which it might perhaps well be referred. 



15. P. marinus, Linn. Eesembling narrow-leaved forms of the last species, 

 low and very leafy : peduncles much elongated : fruit much smaller (a line long) and 

 thinner, round-obovate, not keeled upon the rounded back, tipped with tlie broad 

 sessile stigma : embryo annular. 



Var. (?) OCCidentaliS, Eobbins. Often taller and less leafy : peduncles usually 

 rather short : spikes interrupted : nutlet slightly 3-keeled. — Bot. King Exp. 339. 



The variety only has been collected in Truckee River and Ruby Lake, Northei-n Nevada ( Wat- 

 son), and is apparently a common species of the interior eastward to Montana {liichardson) and 

 Colorado {Hall k Harbour), sometimes nearly approaching European forms. 



16. P. Robbinsii, Oakes. Stem rather stout, often much branched and fre- 

 quently Hexuous : leaves numerous, distichous, the close sheatlis nearly covering the 

 stem, linear-lanceolate, 2 to 3 inches long by 2 lines broad, many-nerved, acuminate, 

 ciliate-serrulate ; stipules obtuse, becoming setose : spikes usually several, on rather 

 stout pedicels about an inch long, loose and more or less interrupted, about half an 

 inch long : fruit oblong-obovate, nearly 2 lines long, keeled with a broadish wing, 

 acutely beaked: embryo stout, ovally annular. — Hov. Mag. vii. 178; Eobbins, in 

 Gray's Manual, 490. 



In ponds and slow streams ; not yet found in California, but to be expected ; Oregon {Hall); 

 Yellowstone region (C. llichardsoii) ; common in the northern Atlantic States. 



Scanty specimens of what seems to be an undescribed species of this grouj) have been collected 

 in Pyramid Lake {Miss S. A. Plummer), without flowers or fruit. The stem is broad and flat- 

 tened ; the leaves thick, 6 inches long by H lines broad, 3-nerved with transverse veinlets, con- 

 spicuously sheathing and with broad stipules^ 



