FLOWERS OF LAKES, RIVERS, ETC. 65 



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

 which form a link between Hydrt)phytes and marsh [)lants and are 

 hygrophilous. 



Most are herbaceous perennials. The majority have creeping- 

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

 Lilv, Water Ikittercup, Starworl. with creeping" stems. A few, such as 

 A'aias, are annual. There are three types of plant-shoots, the rosette 

 type, as in Lobelia; the NympJuca 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 {CaZ/ifric/ic vci'iia). 



The leaf type is floating, as in Water Lilies, Polys^oniim am- 

 pliibiuiii, 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, 

 growth ceasino; when the surface is reached. The Batrachian Ranun- 

 culi are heterophyllous, and able to adopt a terrestrial e.xistence it 

 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 Lsoiites. The nivrioiibvlloid leaf 

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

 like or linear segments, as in Dropwort and Siimi. 



Most aquatics are pollinated above water. Water Lilies and Water 

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

 weed b\' the wind or water, and b)' water in the case of Zauniclicllia, 

 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 hibcrnacula, as Pondweeds, Starwort, &c. 



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

 ceta, Nymphseta, Nuphareta, Batrachieta, Liiuucca, rosette forms. 

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

 each other, and the case with which w.iter plants become helophilous is 

 shown by the ami)hiIjious J'o/yoouniii ainphihiiini, 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 P'ennel dangles its lace-like 



Vcl.. IV. 51 



