86. NAIADACE^E. 171 



85.-LEMNACE.2E. 



1. L^MNA. Duckweed. 



1. L. TRISULCA, L. Ivy -leaved Duckweed. Fronds thin, 

 ^ | of an inch long; narrow, suddenly tapered at the base, blunt, 

 and minutely toothed at the apex; young fronds springing out at 

 right angles from the old ones, on two opposite sides at the base; 

 root single, covered by a terminal sheath (calyptrate). 



Rare. Ponds and still waters. (E) A. 6 7. Very plentiful in Fossil marsh 

 and the Forth and Clyde Canal. 



2. L. MINOR, L. Lesser Duckweed. Fronds broadly oval, 

 compressed, succulent, 3 or 4 together, 1 2 lines long, with a 

 single root covered by a sheath (calyptrate). 



Very common. Stagnant water, covering the surface in large masses. (B) A. 7. 



3. L. POLYKRHIZA, L. Greater Duckweed. Fronds nearly orbi- 

 cular, flat, 3 4 lines in diameter, purple underneath, roots 

 numerous, calyptrate. Fl. have not been found in Britain. (For 

 description of fl., see Hook. & Arn., 8th ed., p. Jfllf.) 



Very rare. On the surface of stagnant water. Forth and Clyde Canal at the 

 now and old wood basins, west from Port-Dundas. (E) A. 



4. L. GIBBA, L. Gibbous Duckweed. Frond nearly flat above, 

 very convex, spongy and pellucid white beneath, cells very large; 

 root solitary, calyptrate; size a little larger than in L. minor. 



Rare. Stagnant water. At the same stations as the former and mixed up with 

 it, (E) A. G-9. 



86. NAIADACE M. 



1. POTAMOG^TON. Pondweed. 



A. Leaves all submerged. 



stipules none. 



1. P. DENSTJS, L. Opposite-leaved Pondweed. Le. short, 

 arranged in 2 rows, thin, pellucid, amplexicaul, broadly lanceolate, 

 keeled below, with a strong midrib, and 2 parallel veins on each 

 side. Ped. very short, reflexed after flowering, bearing 2 3 fl. 

 Nuts rounded and smooth. 



Not common. Lakes and ditches. (E) P. 6 7. "Bardowie loch," HopJc. 

 " Clyde below Hamilton bridge," Pair. Near Blantyre mills. 



** Leaves alternate, stipulate. 

 1. Leaves linear. 



2. P. PUSILLUS, L. Small Pondweed. Stems slender, slightly 

 compressed, much branched. Le. very narrow, linear, acute, with 



