;:c SYSTEMATIC DISTRIBUTION [ch. 



hvpocorvls are common among Raniinculaceae with concrescent 

 conrledons, that is to sav, among forms which supply indica- 

 tions of the ch-iracters of the original Monocotvledonous stock^. 



The ice:, thit the Hclobieae are descended from a very 

 -": f-- cr ur cf Ansiosrerivf, and have inhabited the water 

 for a ccrrespondinglv long period, is rarihed by the ^ct that 

 this series consists of a whole plexus of related femilies, some 

 of which have departed widelv from the original tvi[>e ; it con- 

 tains forms as hn asimder, for instance, as Alisma with its many 

 Ranalean features and Xaias which represents the very acme 

 of flcrs- reduction. One minor piece of e\"iGence favouring the 

 antiquirv of the water habit in the case of the Helobieae, is the 

 fact that this Cohort includes all the marine Angiosperms a 

 biological group which probably originated through the frirther 

 modification of fresh-water tcrrr.?. 



That the Nvmphaeace.-e .\-d the related Ceratopnynaceae 

 on the one hand, and the Hc-obieae on the other, have taken 

 to aquatic life with such conspicuous success, suggests that the 

 original Ranalean stock, from which they both sprang, may 

 have been particularly well adapted to water life. In the Ranun- 

 culaceae the tendency to aquatic habits in the case of the genus 



P uh: is obvious; besides the definitely aquatic sub-genus 



i ;. the Buttercups include a number of forms, such 



i; .h. :.-:. ^r.z R. Fhmmula, which are capable both of 

 laxia ana wiier nie. The singularly slight difierence in general 

 anatomy, between the terrestrial and aquatic species oi Ranun- 

 cmJms, suggests that the land forms are of a tvpe which does 

 not require ^est changes of structure in order to succeed in 

 water life. 



It is a remarkjabie fact that the Syrr.r eti' le tne most highly 

 evolved group of Angiosperms ^has produced no entirely 

 aquatic familv, nor anv singleaquatic species wh: rh has become so 

 for adapted to water :ife as to have acquirec suDmerged hydro- 

 philous |X)llir.2-: : r . The very large family of the Compositae, 

 which may p'trr^r- re classed 25 the ultimate term of the 



- r- - :. E. (1903; and (1908). 



