XXVl] SALVINIACEAE 475 



Oeningen as Pilularia pedunculata is too small to determine 

 with reasonable accuracy. Other supposed representatives of 

 the family mentioned in palaeobotanical literature are not of 

 sufficient importance to describe. 



Salviniaceae. 



The two genera of Salviniaceae, Salvinia and Azolla, are 

 water plants, and are usually described as annuals which survive 

 the less favourable season in the form of detached sporocarps. 

 GoebeP states that all the tropical species of Salvinia known to 

 him have an unlimited existence. 



Salvinia nutans, Hoflfm., the only European species, extends 

 from the South of France to Northern China and the plains of 

 India: the other twelve species are mostly tropical. Azolla, 

 represented by four species, occurs in Western and Southern 

 North America, South America, Madagascar, Australia, New 

 Zealand, and is widely spread in tropical Asia and Africa. 



Species of Azolla frequently form a considerable proportion 

 of the floating carpet of vegetation on inland waters^ growing 

 under conditions which might be supposed favourable for pre- 

 servation in a fossil state. 



The Salviniaceae, though probably rather farther removed 

 than the Marsiliaceae from the homosporous Filicineae, are con- 

 sidered by Bower* to be related to the Gradatae, but modified 

 in consequence of their aquatic habit and the assumption of 

 heterospory. 



No undoubted examples of fossil species of Azolla have 

 been described. Salvinia, on the other hand, is represented by 

 several Tertiary species, for the most part founded on leaves 

 only, and HoUick*, who published a list of fossil Salvinias, has 

 described detached leaves as Salvinia elliptica Newb. from what 

 may be Upper Cretaceous rocks from Carbonado, Washington. 



1 Goebel (05). 



= See Seward (94) p. 441, for a description of the floating plants on the 

 lagunas of Gran Chaco (S. America) by Prof. Graham Kerr. 

 3 Bower (08) p. 611. * Hollick (94). 



