78 ir.OWERS OF LAKES, RIVERS, ETC. 



Essential Si'i;cific Characters: — 



1 6. Nympluca liiica, L. — Leaves siibmcp^ed, wavy, transparent, 

 floating leaves coriaceous, llower yellow, globose, sepals 5, stigmas 

 rayed, not reaching the margin, petals numerous, anthers hypogynous, 

 linear, the fruit a berry. 



Water Cress (Ratlicula Naslurtium aquaiicum, Rt-ndle and 

 15ritten) (= N^asliirtiinii officinale) 



Common and widespread as this plant is, it is not tound in any 

 deposits in which seeds of recent plants are preserved. It is almost 

 cosmopolitan, occurring in luirope, West Asia, North Africa, and it 

 has been introduced into North America, and the colonies of the 

 British Empire, even to the extent of choking some rivers in New 

 Zealand. In the British Isles it is ubiquitous, growing in every vice- 

 county of Great Britain, in Ireland, and the Channel Islands. In the 

 North of England it grows at an altitude of 1000 ft. 



Water Cress, as a rule, is a Hydrophyte growing suijmerged, with 

 its roots alone fixed in tlie mud along the margin of its habitat. But 

 it may also be found growing as a hygrophilous or moisture -loving 

 plant, out of the water on damp mud, at the margin, gravitating, like 

 many so-called truly aquatic plants, between a life on land and a life in 

 the water. It is to be found not only in ditches, ponds, and pools, but 

 also in rivers and lakes. But, as a rule, it is most luxuriant and at its 

 best in shallow running water. 



Water Cress is a large plant when allowed to grow rank, the stem 

 being long but wavy and hollow, and it is seldom or never erect, 

 but like all aquatic plants, when submerged grows lengthwise in, or 

 in this case upon, the water, floating on account of its lightness. 

 At the base it is creeping, and attains a semi-erect habit only at 

 the upper extremity, where the flowering stems rise above the water. 

 At other times it is dwarf, floating, or growing prostrate upon damj) 

 mud. 



It may be recognized by its leaves, with lobes each side of a 

 common stalk, egg-shaped, oblong, leaflets slightly toothed, and nearly 

 heart-shaped at the base, the white flower often finally purple, with 

 petals twice as long as the calyx, w ith round pods with swollen valves, 

 beaded, the pod upturned, and the stigma small. The pods are longer 

 than the flower-stalks, and the seeds are in two rows and flattened 

 lengthwise. 



Water Cress is often as much as 4 ft. long or high. The flowering 



