A LONG-STALKED ELODEA FLOWER 



KOBEET B. WYLIE 



The submersed seed plants are of peculiar interest to the 

 botanist. Obviously descendants of land plants, they offer many 

 ingenious modifications in relation to their adopted habitat. 

 More remotely they were probably derived from some primitive 

 aquatic stock, but all evidences of such ancestry are lost in the 

 multitudinous structures elsewhere associated with land plants. 

 In the life history of each of these aquatic flowering plants there 

 must have been a terrestrial life of sufficient duration to permit 

 the evolution of a dominant sporophyte, the development of 

 heterospory, and the attainment of the seed habit, together with 

 a relatively high degree of floral development. The possession of 

 such structures and habits in common with land plants would 

 argue that our aquatic phenogams are removed but a little from 

 the land. 



Most so-called ' Svater-plants " are only nominally aquatic, 

 living merely rooted in shallow water or partly submersed. The 

 marginal vegetation of everj^ lake affords numerous examples. A 

 few plants, on the other hand, have solved the problems of exist- 

 ence entirely beneath the surface of the water and are truly 

 aquatic since they carry out their whole life history while com- 

 pletely submersed. A fine example is seen in Ceratophyllum 

 demersum L. which is pollinated beneath the surface, so may 

 flourish at considerable depths. In West Okoboji Lake in north- 

 western Iowa this form has been found growing at a depth of 

 nearly thirty feet and is one of the most successful plants in these 

 waters. Zostera and Phyllospadix are marine genera of similar 

 habit. 



An extensive intermediate group includes seed plants that live 

 beneath the surface of the water, but which must bring their 

 flowers to the air if cross pollination is to be effected. Such 

 plants are truly amphibious, though in the reverse sense of the 

 term, since they vegetate in water and seek the air only for aid 

 in reproduction. Vegetatively they are aquatics, but in their 



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