420 



THE ECOLOGY OF PLANTS. 



-^ANTHER 



Fig. 175. Female Flower of Vallisneria 



Spiralis. 



With the anther of an open male flower 

 touching one of its fimbriated stigmas, 

 and an unopened male flower on the left. 



sea- water in which they float until they drift on to the stigmas 

 of the female flowers. In most water plants, however, the 

 flowers are formed above the water and are adapted for 



pollination by wind or by 

 insects; in the former case 

 IGMA much of the pollen falls into 

 the water and is wasted, in 

 the latter the scarcity of 

 insects makes the chance 

 of cross-pollination rather 

 small. 



A few submerged water plants 

 have short stems with a "radi- 

 cal " rosette of more or less 

 cylindrical leaves : Quill- 

 wort (Isoetes lacustris, allied to 

 the ferns and not a flowering 



Elant), with long awl-shaped 

 javes (2-6 inches) which contain 

 four rows of air-chambers and 

 have broad bases usually bearing 

 a spore- case ; Awl wort (Subu- 

 laria, a Crucifer), in shallow 

 edges of mountain lakes, rather exceptional among aquatics in being 

 an annual, a small plant with a tuft of leaves about an inch long ; 

 Water Lobelia (Lobelia dortmanna), in mountain lakes, with cylin- 

 drical leaves 2 or 3 inches long containing two rows of air-chambers ; 

 Shoreweed (Littorella, allied to the Plantains), in sandy or gravelly 

 edges of lakes, when submerged has narrow erect semi -cylindrical 

 leaves and multiplies by runners, but when on mud has shorter and 

 more flattened leaves spreading out ; Water Soldier (Stratiotes, 

 chiefly in E. England), with thick toothed leaves and conspicuous 

 flowers carried on long stalks above the water. 



Some submerged aquatics have ribbon-shaped leaves, which may 

 float on the surface or remain submerged : Vallisneria ; Water Sweet- 

 grass (Glyceria Jluitans) ; Grass-wrack (Zostera), on shores and 

 especially in estuaries, with leaves 1-4 feet long ; Horned Fondweed 

 (Zannichellia), in fresh or brackish pools and ditches, with opposite 

 leaves 1-3 inches long ; and several species of Fondweed (Pota- 

 mogeton). [The Canadian Waterweed (Elodea, or Anacharis), in 

 streams, has narrow pointed leaves about 2 cms. long, arranged in 

 threes on the stems.] Water Star wort (Callitriche) grows very 

 commonly in still waters and is erect, 3-12 inches high ; lower leaves 

 submerged, about 1 inch long, narrow, in spaced-out pairs ; upper 

 leaves broader, forming a rosette at the surface and bearing the small 

 flowers in their axils. 



In the large and variable genus Potamogeton we get species showing 



