790 



THE NAIAD FAMILY. 



broad P. and the various-leaved P. by the sessile, many -nerved lower 

 leaves. 



4. Long Pondweed. 



Fig. 950. 



Potamogeton prselongus, Wulf. 



(Fig. 950.) 

 Bot. Suppl. t. 2858.) 



A large species, with the leaves all sub- 

 merged and thin, with numerous longi- 

 tudinal veins, and a few transverse re- 

 ticulations, like the shining P., but the 

 leaves are broader, all closely sessile, 

 and half-clasping the stem by their 

 rounded base, usually 3 or 4 inches 

 long, obtuse at the tip, and concave, so 

 as to split in drying. Stipules very 

 prominent. Peduncles long and stout, 

 with the flowers and fruits usually larger 

 than in the broad P., in a rather close 

 spike. 



In pools and rivers, generally distri- 

 buted over the globe, except the ex- 

 treme north. In Britain, not so com- 

 mon as the shining P. Fl. summer. 



5. Perfoliate Pondweed. Potamogeton perfoliatus, Linn. 



(Fig. 951.) 



(Eng. Bot. t. 168.) 



Leaves all submerged, thin and many- 

 nerved as in the long P. and the shining 

 P., but much shorter, usually ovate, ob- 

 tuse, completely clasping the stem ; the 

 auricles often united on the opposite 

 side, so that the leaf appears to be 

 pierced through ; from 1 to 1J inches 

 long by full an inch broad. Stipules as 

 in the preceding species, but soon dis- 

 appearing. Spike of flowers seldom 

 above 6 or 8 lines long. 

 In rivers and ponds, all over the north- 

 ern hemisphere, and in Australia. Ge- 

 nerally distributed in Britain. FL sum- 

 mer. 



Fig. 951. 





