IIM^EAN SOCIETY OP lOUDON. XXxix 



by subsequent researcbes, in order to make tbem agree witb pre- 

 conceived tbeories, will carry any stronger conviction to Asa Gray's 

 mind tban to my own, more especially as tbe presumed great anti- 

 quity of tbe Japanese flora is not deduced from tbese facts alone, but 

 is derived also from otber evidences, amongst wbich tbe peculiar 

 cbaracter of the endemic monotypes bears a prominent part. 



With regard to Grisebacb's idea that representative and similar 

 species are independently produced by similarity of climatological 

 conditions, and that they afii'ord no conclusive evidence of community 

 of origin, for that they are to be found in widely dissevered locali- 

 ties between wbich it is impossible to conceive any continuity even 

 in ancient geological periods, and with reference to the instance he 

 adduces of the above-mentioned Heaths of the Cape and of Western 

 Europe, I would recall to your minds some observations I made in my 

 Address of 1869 (p. 25; ' Proceedings,' p. Ixxxvii) on the remark- 

 able coincidence of several genera, and the near similarity of some 

 species that exists between tbese two widely dissevered regions. I 

 would now add that if it is difficult to imagine any ancient continuity 

 which should readily explain this phenomenon, it seems equally 

 difficult to account for it by any climatological similarity, if we 

 consider how much Cape plants in general, accustomed to a pro- 

 longed summer's sun, suffer from its want in the dull damp seasons 

 of Western Europe. 



Another generalization of Grisebacb's, derived from the influence 

 of climatological conditions on the production of species, and affecting 

 the large number of genera in proportion to species of the Japanese 

 region, is, that genera witb numerous species are characteristic of 

 large plant-regions or systems of vegetation-centres which range 

 from west to east, in contradistinction to those which run north and 

 south — that there is in the former much more change in species than 

 in genera, and the reverse in the latter — that we thus fiind very 

 large genera much more readily in Asia than in America (instancing 

 Astragalus as a genus unrivalled in this respect in America). Astra- 

 galus, however, has about one sixth of its species in America, where 

 it ranges from north to south, from the Arctic circle to Southern 

 Chili ; and if we take the list of pbsenogamic genera which have 

 from about 400 to 900 species each {Astragalus, Acacia, Eugenia, 

 Vernonia, Eupatorium, Senecio, Enca, Solanum, Eupliorhia, Pliyl- 

 lanthus, Croton, Piper, Carex, Panicum), none are exclusively 

 Asiatic, and one only, or perhaps two {Astragalus and Carex), have 

 more Europseo-Asiatic tban American species, and range east and 

 west ; five {Eugenia, Vernonia, Eupatorium, Solanum, and Croton 



