152 



Aquatic Organisms 



In this area there are recorded as growing without 

 cultivation 1278 species. Of these 392 grow in the 

 water. However, fewer than forty species grow wholly 

 submerged, with ten or a dozen additional submerged 

 except for floating leaves. Hardly more than an eighth, 



therefore, of the so- 

 called "aquatics" are 

 truly aquatic in mode 

 of life: the remaining 

 seven-eighths grow on 

 shores and in springs, 

 in swamps and bogs, in 

 ditches, pools, etc., 

 where only their roots 

 are constantly wet. 



The aquatic seed 

 plants are representa- 

 tive of a few small and 

 scattered families. In- 

 deed, the only genus 

 having any consider- 

 able number of truly 

 aquatic species is the 

 naiad genus Potamo- 

 geton. Other genera 

 of river- weeds, or true 

 pond weeds, are small, 

 scattered and highly 

 diversified. They bear 

 many earmarks of 

 the special situations 



In the 



Fig. 63. The ruffled pond-weed; Pota- 

 mogeton crispus, one of the most 

 mental of fresh water plants. 



orna- 



independent adaptation to 

 in the water which they severally occupv. 

 economy of nature the Potamogetons or river weeds 

 constitute the most important single group of sub- 

 merged seed plants. They are rooted to the bottom 

 in most shoal waters, and compose the greater part of 



