Potaniacese. 
357 
107. Potamacese. 
532. Potamogeton. Pond-weed. IV, 24. 
1. Ls all opp., clasping, often bent back, oval or lanceo¬ 
late or linear-lanceolate.—Standing and running water; 
distrib. 7. densus L. 2035- 
— Ls altern., only those near the forks almost opp. 2 
2. Ls varying from oval to narrow-lanceolate, but, the upper 
at any rate, never linear . . . . 3 
— Ls exactly linear (grass-like) or bristly, 1 / 2 —5 mm 
broad ......... 11 
3. Ls all petioled, or the lower sessile with narrowed 
base, the upper often floating and then of a different 
form, and always more or less long-petioled . 4= 
— Ls all of the same form, submerged, transparent-mem¬ 
branous and sessile with rounded or half-clasping 
base. (Peduncles almost of equal thickness) . 9 
4. Ls smooth at the edges, the upper always floating, 
leathery; all long-petioled. Peduncles equal in 
thickness to, or hardly thicker than, the stem. Type of 
P. natans ........ 3 
— Ls smooth at the edges, often reddish, the upper fre¬ 
quently floating, petioled, the petioles always shorter 
than the ls; submerged Is always present. Peduncles 
as in the last section ...... 6* 
— Ls more or less rough at the edges, the upper some¬ 
times floating, more or less long-petioled; submerged 
ls always present. Peduncles thickened towards the 
top, distinctly thicker than the stem Type of P. Proteus 
Cham. Schl. . . . . „ . * . . 7 
5. Limb of the submerged ls destroyed by putrefaction 
before the time of flowering, consequently their petioles 
leafless; floating Is (often brownish) oval or oblong, the 
base gen. slightly cordate and, when the limb is stretched 
out in the same plane with the petiole, raised in a 
fold on each side. Petioles slightly hollowed or flat 
above.—Stagnant or slowly flowing water; distrib. 6 
natans L. 2036. 
— Limb of the submerged Is gen. still. r emaini ng at 
the time of flowering; floating ls oval or oblong-lanceo¬ 
late, the base rounded or narrowed and with no fold 
when the limb is stretched in the same plane with the 
petiole. Petioles slightly convex above.—Running water; 
not common. 6 fluitans Roth. 2037. 
6. Ls all petioled, of an equal consistency; submerged ls 
oblong-lanceolate or elliptic; the upper often floating, 
oval or almost orbicular, the base often rounded or 
