66 



NAIADACEAE. 



With propagating buds or glands, or both. 

 With buds, but without glands. 



23- 

 27- 



28. 



Leaves serrulate. 3~7-nerved. 18. 



Leaves entire, with 3 principal and many fine nerves. 19. 



Commonly with glands, but no buds. 



Steins" long-branching from the base; leaves lax, flat, 3-nerved 

 cuspidate. 20. 



Stems simple; leaves strict, revolute, 3-5-nerved. acuminate. 24. 

 With both buds and glands. 



('.lands large and translucent; buds rare, 

 ('.lands small, often dull; buds common. 

 Ieaves linear, 5-7-nerved. 

 Leaves linear. 3-nerved. 

 Leaves capillary, i -nerved or nerveless. 

 Stipules adnate to the leaves or petioles. 



With both floating and submerged leaves. 



Submerged peduncles as long as the spikes, clavate, often recurved. 29. 

 Submerged peduncles none, or at most hardly a line long. 30. 



With submerged leaves only. 



Stigma broad and sessile. 31. 



Style apparent: stigma capitate. 



Fruit without keels or obscurely keeled. 32. 



Fruit strongly 3-keeled. 



Leaves entire, 3-5-nerved. 33. 



Leaves minutely serrulate, finely many-nerved. 34. 



i. Potamogeton natans L,. 



P. crispus. 



P. zosteraefolius. 



, abruptly acute or 

 P. Hill if. 

 P. mtilus. 



22. P. obtusifolins. 



P. Friesii. 



P. pusilliis. 



P. gemtniparus. 



P. diz'ersifolius. 

 P. Spirilltts. 



P. filiform is. 

 P. pectinatus. 



P. interrtiptns. 

 P. Robbinsii. 



Common Floating Ponchveed. (Fig. 142.) 



Potamogeton natans L. Sp. PI. 126. 1753. 



Stems 2-4 long, simple or sparingly branched. 

 Floating leaves thick, the blade ovate, oval or ellip- 

 tic, 2' -4' long, i '-2' wide, usually tipped with a 

 short abrupt point, rounded or subcordate at the 

 base, many-nerved; submerged leaves reduced to 

 phyllodes or bladeless petioles which common ly 

 perish early and are seldom seen at the fruiting 

 period ; stipules sometimes 4' long, acute, 2-keeled ; 

 peduncles as thick as the stem, 2'-4' long; spikes 

 cylindric, very dense, about 2' long; fruit turgid, 

 2 "-2%" long, about \]^" thick, scarcely keeled, 

 narrowly obovoid, slightly curved on the face; 



0^~^/ I! II style broad and facial; nutlet hard, more or less 



/ I pitted or impressed on the sides, 2-grooved on the 



^"""^MR' {r~^- . 1 back; embryo forming an incomplete circle, the 



I 1 Ij ^\ I apex pointing toward the base, 



"j" W I" ponds and streams, throughout North America ex- 



cept the extreme north, extending into Mexico. Also 

 in Europe and Asia. July-Aug. 



2. Potamogeton Oakesianus Robbins. Oakes' Pondweed. (Fig. 143.) 



<//' Oakfsianus Robbins in A. Gray Man 

 H'l- 5, 485- 1867. 



Stems very slender, often much branched from 

 below. Floating leaves elliptic, mostly ob- 

 tuse, rounded or slightly subcordate at the 

 base, i'-2' long, 5 "-9" wide, i2-2o-nerved; 

 petioles 2'-6' long; submerged leaves mere cap- 

 illary phyllodes, often persistent through the 

 flowering season ; peduncles 1'-$' long, com- 

 monly much thicker than the stem, mostly soli- 

 tary; spikes cylindric, .^'-I'long; stipules acute, 

 hardly keeled; fruit obovoid, about i' 2 " long, i" 

 thick, nearly straight on the face, 3-keeled, the 

 middle keel sharp; style apical or subapical; sides 

 of the nutlet not pitted, but sometimes slightly 

 impressed; embryo circle incomplete, the apex 

 pointing toward the base. 



In -till water. Anticosti to northern Pennsylva- 

 nia and New Jersey. Summer. 



