MONOCOTYLEDONS. FLUVLALES. PotCMlOgeton. 193 



2. ZOSTERA. 



Stam. and pistils separated, inserted in two roivs upon one side 

 of a spadix. Spatha foliaceous. Perianth 0. Barren FL 

 Anthers ovate, sessile, alternating with the germens and upon 

 the same spadix. Fertile FL Ovary 1, ovate. Style bifid. 

 Drupe with 1 seed. 



1. Z. marina, leaves entire somewhat 3- nerved, stem roundish. 

 p. 259. Sea-shores. 



3. ZANNICHELLIA. 



Monoecious. Barren FL Perianth 0. Stam. 1. Fertile FL 

 Perianth single, of 1 leaf. Ovaries 4 or more. Style 1. Stig- 

 ma peltate. Caps, sessile. 



1. Zi.falustris, anthers 4-celled, stigmas entire, pericarps tooth- 

 ed on the back. p. 258. Stagnant waters. 



4. POTAMOGETON. 



Flowers perfect, on a spadix arising from a spalha. Perianth 

 (involucre,, Rich. ?). Anthers 4, sessile, alternating with the 

 divisions of the perianth. Ovaries 4. Nuts 4, 1 -seeded, ses- 

 sile. 



* Upper leaves floating. 



1. P. natans, upper leaves floating coriaceous oblongo-ovate pe- 

 tiolate, lower ones membranous lanceolate gradually tapering 

 into a footstalk, p. 57. Lakes. 



2. P. hetei'ophyllum, upper leaves coriaceous elliptical petiolate 

 floating, lower ones membranous linear-lanceolate sessile (pe- 

 duncle clavate, Sm.). p. 57. Lakes. 



3. P.fadtans, upper leaves floating subcoriaceous ovato-lanceo- 

 late tapering into a rather short footstalk, lower ones long lan- 

 ceolate sessile, p. 57. Ditches and lakes. 



** Leaves all submersed. 



4. P. perfoliatum, leaves cordate embracing the stem. p t 58. 

 Rivers and lakes. 



5. P. densum, leaves (all) opposite crowded ovato-acuminate ses- 

 sile, stem forked, spike of about 4 flowers, p. 59. Ditches. 



6. P. lucens, leaves ovato-lanceolate petiolate. p. 58. Rivers 

 and lakes. 



7. P. crisp2tm, leaves lanceolate tapering sessile remarkably 

 waved and crisped serrate, p. 58. Ditches. 



S. P. lanceolatum, leaves linear-lanceolate tapering at the base 



sessile, p. 58. Lakes. 

 9. P. gramineum, fe leaves linear-lanceolate alternate sessile 



broader than the stipules, stem rounded subdichotomous," 



p. 58. Ditches. 



