FLOWERS OF LAKES, RIVERS, ETC. 65 



which there are 20, and we have also included many riparian species 

 which form a link between Hydrophytes and marsh plants and are 

 hygrophilous. 



Most are herbaceous perennials. The majority have creeping 

 stems, and are of clustered, crowded growth, as Mare's Tail, Water 

 Lily, Water Buttercup, Starwort, with creeping stems. A few, such as 

 Naias, are annual. There are three types of plant-shoots, the rosette 

 type, as in Lobelia; the Nymphcea type, as in Water Lilies, with long- 

 stalked, floating leaves; the long-stemmed type with erect stem and 

 internodes, completely submerged, as in Pondweeds, with floating 

 leaves, as in Starwort (Callitriche verna). 



The leaf type is floating, as in Water Lilies, Polygomim am- 

 phibium, Pondweeds, with broad entire leaves and bent margin, pores 

 on the upper surface; and the blade is dorsi-ventral, red below, to 

 retain heat, and the petiole or leaf-stalk adapts itself to the water, 

 ofrowth ceasinof when the surface is reached. The Batrachian Ranun- 



o o 



culi are heterophyllous, and able to adopt a terrestrial existence if 

 need arise. 



The submerged leaf may be zosteroid or ribbon-like, as in Bur-reed, 

 some Pond-weeds, caused by deep or running water, some marsh 

 plants acquiring them if necessary, and the Bulrush has current 

 leaves half a yard in length. The elodioid leaf is narrow, flat, stalk- 

 less, entire, as in Elodea, Mare's Tail, &c. The isoetoid leaf is linear, 

 undivided, rounded, and tubular, as in Isoetes. The myriophylloid leaf 

 is whorled, as in Water Milfoil, or consists of leaves divided into thread- 

 like or linear segments, as in Dropwort and Stum. 



Most aquatics are pollinated above water. Water Lilies and Water 

 Violet are pollinated by insects; Mare's Tail, Water Milfoil, and Pond- 

 weed by the wind or water, and by water in the case of Zannichellia, 

 Starwort, Naias. Subularia, Limosella, and some Batrachian or 

 Water Buttercups, &c., are cleistogamic. The fruits or seeds are 

 dispersed by the water. Reproduction is largely vegetative. Many 

 plants develop hibernacula, as Pondweeds, Starwort, &c. 



Associations arranged in zones may be recognized as Algae, Chara- 

 ceta, Nymphaeeta, Nuphareta, Batrachieta, Limneea, rosette forms, 

 Lobelia, &c. The Hydrocharis and Limnaea formations merge into 

 each other, and the ease with which water plants become helophilous is 

 shown by the amphibious Polygonum ainphibiiun, by Water Cress, and 

 the Water Plantain. 



Along the margins of the rivers tall clumps of sulphur blooms of 

 Meadow Rue line the waterway. Water Fennel dangles its lace-like 



51 



