xxv] SYMPETALAE AND MONOCOTYLEDONS 313 



plants as Menyanthes, the Bog Bean, form a transition to the 

 typically aquatic genus Limnanthemum. 



The Scrophulariaceae include several hydrophytic genera; 

 heterophyllous species are found in Ambulia (Limnophila) and 

 Hydrotriche. In Britain the water Scrophulariaceae are re- 

 presented by Limosella aquatica^ a small plant whose corolla 

 scarcely exceeds the calyx in length, while its capsule sometimes 

 fails to dehisce ; these features are no doubt symptoms of the 

 reduction so often associated with aquatic life. 



The Bladderworts ( Utricularia\ belonging to the Lenfibularia- 

 ceae, contain a number of species which are aquatic, besides 

 others which live on dry land. The terrestrial Plantagos, whose 

 anemophilous flowers are generally regarded as reduced from 

 the Scrophulariaceous type, form a transition to the aquatic 

 genus Littorella in which floral reduction has reached a still 

 higher pitch; the flowers are unisexual with a one-seeded in- 

 dehiscent fruit. Limnosipanea is an example of a Rubiaceous 

 hydrophyte. 



Among the otherwise terrestrial Campanulaceae, we find the 

 submerged Lobelia Dortmanna, while the Compositae include 

 a few hydrophytes 1 such as Bidens Beckii a heterophyllous 

 water plant from North America and Cotula myriophylloides. 



Passing to the Monocotyledons which the present writer 

 regards as a phylum comparable with the Dicotyledons in being 

 ultimately derived from ancestral forms of the dicotylar Rana- 

 lean plexus we are at once struck with the relatively high 

 number of aquatic families. The Helobieae (or Fluviales) con- 

 sist of a series of families which are generally grouped together, 

 chiefly on account of the enlarged hypocotyl of their embryo, 

 which forms a remarkable common character. The aquatic and 

 marsh families generally included in the Cohort are the Alisma- 

 ceae, Butomaceae, Hydrocharitaceae, Aponogetonaceae, Junca- 

 ginaceae, Potamogetonaceae and Naiadaceae. The Alisma- 

 ceae, which appear to be the most primitive of the group, show 

 striking similarities to the Ranunculaceae, which they re- 

 1 Hutchinson, J. (1916). 



