JOURNAL 



OF THE 



Royal Hoiitioultuml Society. 



Vol. XXXVII. 1911. 

 Part II. 



THE OEIGIN OF MONOCOTYLEDONS FEOM AQUATIC 

 DICOTYLEDONS. 



By THE Eev. Professoe G. Henslow, M.A., F.L.S., V.M.H. 



[Read June 20, 1911.] 



A VERY general conviction is now prevalent among botanists that 

 Monocotyledons were, somehow,- derived from Dicotyledons, for fossil 

 botany has shown that the first flowering plants or Gymnosperms 

 were undoubtedly derived by descent from ferns or at least fern- allies, 

 such as the Cycadofilices and Cycadophyta.'^' Although no actual 

 member of the most primitive Angiosperms with a closed up ovary 

 bearing a style with stigmas is at present known, yet since the former 

 are mostly dicotyledonous, it is a justifiable conclusion that the class 

 Dicotyledons was the first of the Angiosperms to be evolved. 

 Numerous writers have called attention to very many morphological 

 and anatomical features of Monocotyledons, which are paralleled by 

 similar ones in aquatic Dicotyledons; for it is noticeable that the 

 greater number of species referred to by writers are dicotyledonous 

 water-plants. 



My object is to show that all such coincidences, taken collectively, 

 prove incontestably that Monocotyledons were actually descended from 

 aquatic Dicotyledons. The proof is, of course, mainly inductive; i.e., 

 it rests upon a vast accumulation of agreements or coincidences 

 between them. Not only does this concern the aquatic species of the 

 two classes, upon which water acts alike, but all terrestrial Mono- 

 cotyledons were ancestrally aquatic ; later, on recovering their position 

 on dry land, they merely re-adapted themselves to air, by altering the 

 internal anatomy and external epidermis so as to become denizens of 



* Studies in Fossil Botany, D. H. Scott. 11. pp. 498, 604. 

 VOL. XXXVII. U 



