CHAPTER XVIII 



THE FLOWERS OF WATER PLANTS AND THEIR 

 RELATION TO THE ENVIRONMENT 



THE most notable characteristic of the flowers of the 

 majority of aquatic Angiosperms is that they make sin- 

 gularly little concession to the aquatic medium, but display the 

 utmost conservatism in form and structure. The plants which 

 have, in the course of evolution, adopted water life, have, as 

 we have already shown, profoundly modified their vegetative 

 organs in connexion with their new environment, but their 

 methods of sexual reproduction in general depart little from 

 those which had already become stereotyped in their terrestrial 

 ancestors. This sharp distinction, between the degree of modi- 

 fication of the vegetative and reproductive parts, is particularly 

 well shown in the case of so highly specialised a water plant 

 as Utricularia vulgaris. Here the vegetative body is entirely 

 submerged, but the aerial inflorescence axis and the flowers, 

 which are adapted to entomophilous pollination, in no way differ 

 from those of a terrestrial plant. The extreme divergence in 

 mode of life, and even in internal structure, between the 

 aerial reproductive region and the submerged vegetative region 

 in this species, led an anatomist to speak of the plant as con- 

 sisting of "an aquatic being, vegetating horizontally without 

 roots," and "a vertical aerial being, producing flowers at its 

 apex, and implanted in the first, which serves it as soil, or 

 rather as roots 1 ." 



Those hydrophytes which still retain a type of flower adapted 

 for aerial life, are under the absolute necessity of raising their 

 inflorescence axis well above the water level, if cross-pollination 

 is to be secured. This is sometimes very incompletely achieved, 



iTieghem, P. van (1868). 



152 



