in the conspicuous Habenaria repens. It is commonly formed on species of 

 Ludwigia, Aeschynomone, Ly thrum, Ammannia, Peplis and Sesbania. 



The organs and means of sexual reproduction in the vast majority of vascular 

 hydrophytes are not unlike those of strictly terrestrial plants. Only a relatively 

 few of our hydrophytes have wholly submerged hydrophilous flowers. Of these, 

 those occurring in our region are Ceratophyllwn, Najas, Ruppia, Zannichellia, 

 Posidonia, Cymodocea, Halophila, Thalassia, Halodule and several species of 

 Callitriche. 



Besides sexual reproduction many hydrophytes have a capacity for vigorous 

 vegetative reproduction, and this has been found to be exceptionally high in 

 many genera. The means, however, of vegetative reproduction is apparently no 

 different from those found in strictly terrestrial species. These include the capacity 

 to regenerate from small vegetative fragments, especially if they have attached 

 buds, and the production of tubers, rhizomes, stolons, turions, dormant apices 

 and offsets. The ease of dispersal of these propagules by various agents, such as 

 floods, waterfowl, animals, motorboat propellors, irrigation activities and the 

 other direct actions of man account for the wide distribution of many aquatic 

 plants. 



The stems, rhizomes, stolons, runners, petioles and peduncles of most sub- 

 merged aquatic plants are notoriously brittle. Because of this brittleness even a 

 slight disturbance, much less a violent one, will frequently cause fragmentation of 

 the plant body. This is especially true of species in the genera Ceratophyllum, 

 Egeria, Elodea, Myriophyllum and Najas. The same is also true to some extent 

 for species of Callitriche, Azolla, Utricularia and in the Lemnaceae. Another 

 method of vegetative reproduction is exhibited by Ceratopteris (Fig. 22), wherein 

 plants, by means of gemmipary, arise from buds near vein-endings at the base of 

 marginal notches in mature leaves. This method of vegetative reproduction is 

 also common to some cruciferous species, such as in Armoracia, Cardamine and 

 Rorippa. 



All types of rhizomes may be found in aquatic plants. These may be woody or 

 herbaceous, spongy or firm, slender or enlarged, widely creeping or much-abbre- 

 viated. Some species, especially in Cyperus, Potamogeton and Sagittaria produce 

 stem tubers from which they perennate. These tubers, which are frequently near 

 or just below the surface of mud, provide food for water fowl, especially geese. 



In Nymphoides (Fig. 1), the buried rootstock gives rise to long stems that 

 trail through the water and gradually ascending to the surface to produce short- 

 petioled leaves from their terminal nodes along with clusters of aerial flowers. A 

 cluster of adventitious swollen, banana-shaped roots is produced from the node 

 at the base of this floating rosette. Upon decay of the ascending stem the cluster 

 of tuberous roots is set free and subsequently regenerates a new plant. 



Among those ordinarily dryland plants that apparently depend upon an excess 

 of water during at least a part of their life-span are Heliotropium molle and H. 

 glabriusculum, which grow where water temporarily accumulates after rains. These 

 plants have evolved abundant corky tissue in their seeds that make them well- 

 adapted for water dispersal. When observed during much of their life-span, how- 

 ever, one might wonder why these species should be included in a work on aquatic 

 and wetland plants for they grow in usually somewhat desertic situations. 



The principal agents that influence plant dispersal are water, animals, wind and 

 man. Dispersal of strictly aquatic plants are undoubtedly influenced more by 

 water and animals than by wind and man. Buoyant fruits and seeds, and vegeta- 

 tive propagules broken from plants by turbulence may be carried great distances 

 by currents and wave action. 



The transmission of vegetative fragments and seeds in the plumage and on the 

 muddy feet of waterfowl undoubtedly accounts for the wide distribution of some 



