WEEDS OF PONDS, RIVERS, DITCHES 331 



has spikes of dull purple labiate flowers. The root- 

 stock creeps extensively, and from it grow upright 

 stems i^ to 2 feet high, with somewhat narrow ovate- 

 lanceolate and almost sessile leaves. 



POLYGONACEJi 



Great Water-dock (Rumex Hydrolapathum Huds.)isa 

 widely distributed and characteristic river-side plant, and 

 the largest of the British 

 Docks. The stems are 

 stout, branched, and 3 

 to 5 feet high, with 

 oblong-lanceolate leaves, 

 which are cordate at the 

 base, and sometimes 

 more than a foot long. 

 The flowering panicle is 

 leafless, with crowded 

 whorls of flowers. 



CERATOPHYLLACE^: 



Hornwort (Cerato- 

 phyllum demersum L.) is 

 a locally distributed 

 aquatic plant, com- 

 pletely submerged in 

 the water of ponds and 

 ditches. It possesses 

 long slender stems and 

 leaves in whorls (Fig. 

 94). The leaves are 

 usually dark green, much divided into narrow, toothed 

 segments, and about an inch long. The flowers are 



FIG. 94. Hornwort (Ceratophyllum 

 demersum L.), x. 



