NAIADES. 



79-1 



6. Curly Pondweed. Potamogeton crispus, Linn. 

 (Fig. 952.) 



(Eng. Bot. t. 1012, the leaves too much lobed.) 



One of the most marked of the alter- 

 nate-leayed species. Leaves all sub- 

 merged and thin, narrow-oblong or 

 broadly linear, obtuse, shortly tapering 

 at the base, 1 to 2 inches long, 3 to 5 

 lines broad, always waved and sinuated 

 on their edges, and marked by 1 strong 

 midrib and 2 parallel slender nerves at 

 some distance from it, but connected 

 with it by a few transverse veins. Spikes 

 small, consisting of about 3 to 6 flowers, 

 at some distance from each other. 



In ponds, streams, and ditches, through- 

 out Europe and central and Russian 

 Asia, except the extreme north. Com- 

 mon in Britain. Fl. summer. 



Fig. 952. 



7. Opposite Pondweed. Potamogeton densus, Linn. 

 (Fig. 953.) 



(Eng. Bot. t. 397.) 



Eeadily known by its numerous short 

 leaves, all opposite, and arranged in two 

 rows on opposite sides of the stem ; they 

 are all submerged and thin, broadly lan- 

 ceolate, 6 to 9 lines long, folded and 

 clasping the stem at their base, with 

 a strong midrib and 2 fainter parallel 

 nerves, connected by a few transverse 

 veins. Stipules only under the peduncles 

 or branches. Peduncles very short, 

 turned down after flowering, bearing a 

 head of 2 or 3 flowers only. Eipe car- 

 pels rather large, rcunded, and smooth. 



In shallow pools, and ditches, all over 

 Europe, except the extreme north. Com- 

 mon in Britain. Fl. summer. 



Fig. 953. 



