480 cv. NAIADACE^E. [ Potamogeton . 
somewhat lax, stem capillary nearly terete. Ch. et Schlecht. 
1. c. p. 175. 
Ponds and ditches at Bexley near Norwich, y. 7, 8. — We have 
seen no British specimens, nor are we at all satisfied that the foreign 
ones are specifically distinct from the next species, with which 
Kunth also is inclined to unite them. The fruit has an obscure 
tooth on the ventral suture near the base, which has not been 
observed in P. pusillus. Mr. Bentham considers all of this section to 
form only one natural species, which he calls P. pusillus, a name 
however not very applicable to some of the forms. 
[Mr. Babington mentions a plant found near Dunstanburg, 
Northumberland, that he supposes to be P. gracilis Fr., “ which has 
1-nerved attenuate-cuspidate leaves, terete stems, and globose-elliptical 
fruit without a keel.” We have seen no specimens. P. gracilis Fr. is 
however reduced by Reiciienbach (Ic. FI. Germ. vii. p. 14, n. 39) 
to the next species, of which he considers it a variety with very 
narrow 1-nerved leaves.] 
5. P. pusillus L. ( small P .) ; leaves narrow-linear 3 — 5- 
nerved with obscure connecting veins, peduncles 2 — 3 times 
longer than the somewhat lax spike, stem slightly compressed. 
— a. leaves 3-nerved, nerves in the middle between the midrib 
and the margin. E. B. t. 215. — /L leaves broader with an 
accessory nerve on each side between the margin and the 
primary lateral ones. P. compressus L. : E. B. t. 418. 
Ditches and still waters. y. 6, 7 . — The leaves are more or less 
acute; the spikes oblong, compact or a little interrupted. We quite 
agree with Chamisso and Schlechtendal, who unite P. compressus 
with P. pusillus. 
6. P. gramineus L. ( grassy P .) ; leaves broadly linear obtuse 
3-nerved with few and obscure connecting veins, peduncle 
scarcely longer than the oblong oval dense spike, stem slightly 
compressed. E. B. t. 2253. P. obtusifolius Mert. et Koch. 
Ponds and ditches. Amberley, Sussex ; Orford, near Warrington, 
Lancashire; Arburv Hall, Warwickshire; Deptford; Norwich; 
Castle- Howard and Beverley, Yorkshire. Possil marsh, near Glas- 
gow ; Kincardineshire, y. 7 . — Nearly allied to the last, but stouter, 
darker-coloured, and with short peduncles, scarcely longer than the 
stipule of the leaf from the axil of wh ich they spring. The middle nerve 
or rib is accompanied by many parallel oblong reticulations both in this 
and the last species ; but there are none of the numerous longitudinal 
parallel intermediate nerves seen in the two following. Occasionally 
the peduncles are nearly twice the length of the spike, when it 
becomes very difficult to distinguish this from var. P. of the last 
species, with which it agrees in general appearance; but we believe 
tiiat the latter has always the two supplementary nerves, whereas 
P. gramineus has the leaves only 3-nerved. Judging from the speci- ! 
mens we have seen in herbaria, P. gramineus is more common than 
P. pusillus &., while P. pusillus a. is more common than either of the 
others. 
