238 FLOWERS OF AQUATICS [ch. xviii 



elongation of the elastic and thread-like pedicles of the colony- 

 kept the pollen-grains in constant motion, which left me no 

 doubt that at times the grains would be directly borne to the 

 stigmatoid appendages of the pistilliferous flowers." 



It seems to the present writer conceivable that, in future 

 phases of evolution, if more Angiosperms reach the highly 

 specialised stage of complete submergence, the water fauna may 

 come to play an important part in their pollination. There may 

 even arise a parallelism of development and an interdependence 

 between aquatic animals and submerged plants comparable with 

 that which has obtained in the case of aerial insects and the 

 flowers which they pollinate! 



In general, the consideration of the flowers of hydrophytes 

 seems to lead to the conclusion that submerged pollination is a 

 relatively modern development. It is, from some points of view, 

 merely a further advance on lines similar to those already 

 marked out in the case of anemophily. The great majority of 

 hydrophilous plants have near relatives sometimes even mem- 

 bers of the same genus which retain anemophilous or entomo- 

 philous habits; this may be regarded as a proof that plants with 

 submerged pollination have arisen in comparatively recent 

 times from ancestors with the aerial type of flower. Ceratophyl- 

 lum forms an exception, since it is entirely hydrophilous, and 

 has no intimate affinities with any other genus. It is probable, 

 from its extreme adaptation to aquatic conditions and its isolated 

 position in the relatively primitive Ranalean plexus, that it is a 

 genus whose ancestors took to aquatic life at a very early stage 

 in the race history of the Angiosperms. 



