792 



THE NAIAD FAMILY. 



8. Slender Pondweed. Potamogeton pusillus, Linn. 

 (Fig. 954.) 



(Eng. Bot. t. 215, P. compressus, t. 418, P. graminrus, t. 2253, 

 P. trichoides, Bab. Man.) 



Distinguished from all the preceding 

 species by the thread-like stems, and 

 very narrow-linear leaves, like those of 

 Zannichellia or Ruppia, and from the 

 following by the scarious sheathing sti- 

 pules, always observable in the axils of 

 those leaves at least which are under the 

 branches or peduncles. Leaves veined 

 as in the Fennel P., 1 to 3 inches long 

 and very seldom a line broad. Peduncles 

 slender, with a short, close spike of small 

 flowers. Nuts small, ovoid, almost 

 pointed, with a more or less strongly 

 marked dorsal rib. 



In pools, ditches, and still waters, 

 fresh or salt, almost all over the world. 

 Common in Britain. Fl. summer. The 

 P. acutifolius (Eng. Bot. Suppl. t. 2609) 

 and the P. zoster cefolius (Suppl. t. 2685) appear to represent a robust 

 variety of this species, or the latter perhaps a state of the various- 

 leaved P., without the upper floating leaves. In both the leaves are 

 3-nerved only. 



Fig. 954. 



9. Fennel Pondweed. Potamogeton pectinatus, Linn. 

 (Fig. 955.) 



(Eng. Bot. t. 323. P.filtformis, Brit. Fl.) 



Stems thread-like, with very narrow, grass -like leaves, usually 2 or 

 3 inches long, most of them dilated at the base into a rather long 

 sheath, which is scarious at the edge and often projecting at the top 

 into two small scarious lobes, these scarious edges supposed to be 

 stipules adhering to the base of the leaf ; the sheathing stipules of the 

 other species either wholly wanting or very rare under the peduncles. 

 The midrib of the leaf sometimes separates into longitudinal, netted 

 veins, only visible under a magnifying-glass, and there are usually 2 



