426 THE NAIAD FAMILY. [Potamogeton. 
on an axillary peduncle rising above the water. Perianth of 4 scale- 
like segments. Stamens 4, opposite the segments ; the anthers sessile 
and 2-celled. Capsules 4, each with a very short style or a sessile 
stigma. Nuts small and seed-like, sessile, usually laterally compressed. 
Seed much curved or almost coiled round an obovoid projection of the 
endocarp. 
A considerable genus, most of the species spread over the greater 
part of the globe, chiefly in fresh water, but some accommodating 
themselves also to salt water, and many of them very variable in foliage. 
In the species with axillary stipules, these are sometimes only to be 
seen under the peduncles or under the branches of the stem. 
Upper leaves on long stalks, floating on the surface of the 
water. 
Lower submerged leaves stalked or reduced to mere leaf- 
stalks . ; : : . lL. Pi natons: 
Lower submerged leaves sessile or nearly SO. 
Lower submerged leaves linear, 1-nerved or arenes 3- 
nerved 
: - P. heterophyllus. 
Lowers submerged leaves lanceolate, with | Ds q, or more 
nerves. . P. lucens. 
All the leaves under water and sessile. 
Leaves all opposite . P. densus. 
Leaves alternate, except under the peduncles or forks. | 
Leaves broadly ovate, clasping the stem all round 
Leaves ovate-lanceolate or oblong, broad at the base and 
clasping the stem 
Leaves lanceolate or linear, tapering at the base, or not 
stem-clasping. 
Leaves broadly linear or lanceolate, flat and entire, with 
. P. perfoliatus. 
pep OF NN w Ww 
. P. prelongus. 
many nerves . &. F. lgeens: 
Leaves broadly-linear, waved, 1- or 3-nerved 6. P. erispus. 
Leaves narrow-linear, not waved, 1- or 3-nerved. 
Leaves not dilated ‘at: the base, with a scarious stipule 
in most axils. 
Leaves 1 to 2 lines broad. Nuts 1} lines long. 
Leaves obtuse or scarcely acute. Spikes usually 4 
inch long . : ; ; : ; : f . 8. P. obtusifolius. 
Leaves very acute. Spikes short and few-flowered . 9. P. acutifolius. 
Leaves under 1 line broad. Nuts underllinelong . 10. P. pusillus. 
Leaves dilated at the base into a sheath, scarious at the 
edges ; : : : : : : : ; . 11. P. pectinatus. 
[The Potamogetons, like so many water plants, are very difficult of dis- 
crimination, and nearly thirty species are enumerated in the London 
Catalogue of 1886 as British, many of them distinguished by very 
variable or minute characters. I have been unable to reduce these 
satisfactorily to the leading types which Bentham has confined himself 
to describing. | 
1. P. natans, Linn. (fig. 958). Broad P.—One of the largest of our 
Potamogetons. Leaves stalked, the upper ones floating on the surface 
of the water, of a thick, opaque texture, ovate or oblong, 2 to 4 inches 
long by 1 to 14 broad, usually rounded at the base but sometimes 
cordate or tapering, marked by several longitudinal nerves, with a few 
cross veins often branched or slightly netted; the submerged leaves 
thinner and narrower, but stalked like the floating ones or reduced to 
a mere stalk. Axillary stipules closely sheathing, often an inch long. 
Spike dense and cylindrical, often an inch long or more, on a stout 
peduncle of several inches. Nuts ovoid, above a line long, slightly com- 
