xvm] CLEISTOGAMY 233 



entomophily associated with the water habit, since the immedi- 

 ate ancestors of Littorella were most likely closely related to the 

 typically wind-pollinated Plantagos. 



The difficulty of keeping entomophilous or anemophilous 

 flowers above water seems to have led, in the case of certain 

 aquatics, to the formation of cleistogamic flowers which can 

 set seed even when submerged. But Prankerd's 1 work has 

 suggested that records of cases of cleistogamy among water 

 plants ought to be received with some caution, unless they are 

 based on evidence of a highly critical nature. Concerning the 

 Water Violet, this author writes, " Cleistogamy has been attri- 

 buted to Hottonia^ but I have found no trace of it during three 

 summers' field work. The idea is probably due to some small, 

 closed flowers, which occur sometimes among those fully 

 developed, but serial sections have shown that these are merely 

 abortive." It is possible that similar detailed investigations of 

 other water plants, which have the reputation of bearing cleisto- 

 gamic flowers, might considerably reduce the list; Subularia for 

 instance, which has been called cleistogamic, seems to open its 

 flowers even if submerged 2 . There are however a certain number 

 of cases in which the existence of cleistogamy is adequately 

 established. Hooker 3 , for example, described the phenomenon 

 in detail in Limosella aquatica, L. This plant in Kerguelen's 

 Land was, he writes, "found in the muddy bottom of a lake, 

 and probably flowers all the year round. I gathered it in the 

 month of July (mid- winter), beneath two feet of water, covered 

 with two inches of ice; even then it had fully-formed flowers, 

 whose closely imbricating petals retained a bubble of air, the 

 anthers were full of pollen and the ovules apparently impreg- 

 nated. The climate of Kerguelen's Land being such, that this 

 lake is perhaps never dried, it follows that the plant has here the 

 power of impregnation when cut off from a free communication 

 with the atmosphere, and supplied with a very small portion of 

 atmospheric air, generated by itself." Ranunculus fluitans, Lmk., 



1 Prankerd, T. L. (1911). 2 Hiltner, L. (1886). 



3 Hooker,J. D. (1847). 



