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NOTES ON PONDWEEDS.
By Alfrkd Fryer.
PoTAMOGETON cRispus L. — Rootstock terete, slender, creeping,
shallow-rooting ; stem compressed, obscurely quadrangular, guttered
on the flattened sides, rounded on the edges ; simple below,
branched above, and with short branchlets springing from the axil
of each leaf on the main stem. Leaves all similar, strap-shaped,
oblong, alternate, or sometimes opposite at the base of the branches
and in the upper part of the stem, rounded and semi-amplexicaul,
or slightly narrowed and sessile at the base ; struwjli/ unduhded,
crisped, serrulate, blunt, or narrowed towards the apex, without a
distinct mucro, flat and very finely serrulate on young submerged
growths ; with three prominent ribs, upper with two fainter ribs
near the margin connected by distant oblique veins ; brownish
green, tinged with red or purple or bright green, translucent,
shining, somewhat horny. Stipules small, very short, lacerated at
the apex, scarious, not persistent. Peduncles slightly curved,
springing from the forks of the branches, or lateral, rarely subtended
by opposite leaves, compressed like the stem, but not channelled
except in tlie slightly tapering upper part ; as long as or longer
than the subtending foliage. Spike short, few-flowered. Drupelets
(fresh) acuminate, with a lou'j beak equalling or exceeding the nut
central keel sVujhtlij n-imjed and crested, with a conspicuous jieshy tooth
at the base almost parallel with the axis of the fruit, lateral ridges
obscure, blunt. Whole plant submerged except the spikes, which
are sustained for some time above the water even when in fruit.
P. cri.spns is easily distinguished from all hitherto described
British pondweeds by its compressed stem, and by its remarkably longbeaked
fleshy fruit ; also, in the ordinary state, by its strongly undulated
crisped leaves. It is rarely, however, that the leaves are so conspicuously
curled as in the specimen represented in 'English Botany
(ed. 3, pi. 1413) ; I have only once collected this extreme state.
The plant begins to grow in late autumn, and continues growing
throughout the winter ; the youug shoots, especially on the deeply
submerged barren branches, liave flat and narrow leaves, which
liave much the appearance of those of P. obtus[folius or of P. Friesii,
but may be known from those of all the species of " graminifolii " by
their finely serrulate but not jinttencd margins, and the branches by
their compressed stems. Authors generally consider that Hudson's
P. serratus {P. crispus var. serratus Lond. Cat. ed. 8) was founded
on this young state of P. cris/ius ; perhaps, however, it would be
better to restrict the name of P. serratus to a small flat-leaved form
of the species which is distinguished by its finely serrulate flat,
narrow, strap-shaped leaves even whun the plant is in fruit.
Possibly this form may be a true variety of crLfjius ; but, as far as 1
have been able to observe it in the Fens, where in some districts it
is common, it is more probably a .