S6 HYDROCHARITACEAE [ch. 



which the pollination has been described in detail, the sub- 

 merged male buds are found to be each occupied by a bubble of 

 gas, probably carbon dioxide. Directly the flower reaches the 



^M.S.deL 



Fig. 35. Elodea ioensis, Wylie. i, open staminate flower attached to plant. 



2, mature staminate flower enclosed within the spathe. 3, staminate flower 



emerging from the spathe. 4, detached and empty staminate flower floating on 



the water with elongated axis trailing. [Wylie, R. B. {191 2).] 



surface by the elongation of its filiform axis^, it opens suddenly 

 and at the same moment the pollen sacs dehisce explosively. It 

 thus comes about that abundant pollen floats on the surface of 

 ^ This axis is mentioned by Caspary, R. (1858^) with the incorrect de- 

 scription " tubus calicis filiformis." 



