788 



THE NAIAD FAMILY. 



1. Broad Pondweed. Potamogeton natans, Linn. 

 (Fig. 917.) 



(Eng. Bot. t. 1822, P. oblongus, Suppl. t. 2849. P. poly gonif alius, 

 Bab. Man.) 



One of the largest of our Pondweeds. 

 Leaves stalked, the upper ones floating 

 on the surface of the water, of a thick, 

 opaque texture, ovate or oblong, 2 to 4 

 inches long by 1 to 1§ broad, usually 

 rounded at the base, sometimes cordate 

 or tapering, marked by several longi- 

 tudinal nerves, with a few cross-veins 

 often branched or slightly netted ; the 

 submerged leaves thinner and narrower, 

 but all stalked or reduced to a mere 

 stalk. Axillary stipules closely sheath- 

 ing, often an inch long. Spike dense 

 and cylindrical, often an inch long or 

 more, on a stout peduncle of several 

 inches. Nuts ovoid, above a line long, 

 slightly compressed, nearly straight, 

 the inner edge rounded outwards, with 

 1 or sometimes 3 dorsal ribs. 



In stagnant or running waters, deep 

 or shallow, sunny or shaded, in almost all parts of the world, and 

 varies accordingly in the size, shape, and texture of the foliage, the size 

 and number of the flowers, fruits, etc. Abundant in Britain. Fl. 

 summer. A variety with the leaves all under water, thin and almost 

 transparent, although stalked and broad, and with smaller spikes and 

 fruits, is often admitted as a species, under the name of P. planta- 

 gineus (Eng. Bot. Suppl. t. 2848). 



Fig. 947. 



2. Various-leaved Pondweed. Potamogeton heterophyllus, 



Schreb. (Fig. 948.) 



(Eng. Bot. t. 1285.) 



Usually much smaller than the broad P., which it resembles in the 

 long stalk and the ovate or oblong shape of its floating leaves, but 

 these are only 1 to 2 inches long, and the submerged leaves are all 

 narrow-lanceolate or linear, with the few veins of the slender P., 

 tapering at both ends but not distinctly stalked. Spikes and fruits 

 like those of the smaller forms of the broad P. 



