NAIADACEiE. 49 



nearly simple and scarcely dicliotomous. Leaves all similar, sessile, 

 linear, narrowed towards the base, shortly acuminate-cuspidate, with 

 5 (rai-ely 3) longitudinal ribs without faint ones between them, mostly 

 with axillary fixscicles of smaller leaves. Stipules small, acuminate 

 or acute, scarious, with numerous rather slender longitudinal fibres. 

 Peduncles terminal between the forks of the stem (but the lower ones 

 pseudo-axillary, from one of the forks being reduced to a fascicle of 

 leaves), longer than the spike, usually twice or thrice as long, rather 

 slender, shghtly thickened upwards. Sepals with their lamina sub- 

 orbicular. Pistils 4. f ruitmg-spike cylindrical-oblong, slightly inter- 

 rupted, few-tiowered. Fruit rather small, brownish-olive, slightly 

 compressed, acuminated, convex on the upper margin, on which there 

 is no tooth, half oval and bluntly 3-keeled on the back, terminated 

 by a rather short central slightly recurved beak. Plant rather dull 

 green, i*etaining its coloiir when dried. 



In ponds and ditches. Apparently rare. I have found it myself 

 only on Wray Common, near Keigate, where it is now extinct by 

 drainage. Besides this, I have specimens from Stoke Heath, War- 

 rington. It has been so much confounded with large forms of P. 

 pusillus that I do not venture to quote stations from which I have 

 not seen specimens. 



England, [Scotland ? Ireland ?]. Perennial. Summer. 



Very similar in general aspect to P. gramineus, but the leaves are 

 usually longer and much more distant, the stems much more flattened 

 and less branched, the greater number of branches being reduced 

 merely to fascicles of leaves. The leaves are acuminate-cuspidate, and 

 have two more ribs than those of P. obtusifolius, though the two next 

 the margin of the leaf are said to be sometimes absent. The peduncles 

 (exclusive of the spike) are, in fruit, f to 1^ mch long, the spike ^ 

 to }j inch, distinctly interrupted. The fruit is considerably smaller, 

 scarcely -^ inch long, bulging out towards the apex on the upper side, 

 and with the margin forming less than a semicircle on the lower; the 

 beak conspicuous, about -} of the length of the fruit. Whether this 

 be really distinct from P. pusillus, I have seen too few specimens to 

 enable me to decide. 



Flat-stemmed Pondweed. 



German, Stachehjntziges Samkraut. 



SPECIES XX.-POTAMOGETON PUSILLUS. Lhm. 

 Plate MCCCCXIX. 

 Billof, Fl. Gall, et Germ. Exsicc. No. 653. 



Stem subcylindrical, not compressed, fiUform, subdichotomous. 



VOL. IX. u 



