the result to its legitimate issue. "It might not, perhaps," he 

 observes, "be difficult to find two points in the United States and 

 in Europe, or in equinoctial America and Africa, which present 

 all the same circumstances ; as, for example, the same tempera- 

 ture, the same height above the sea, a similar soil, an equal 

 amount of humidity. Yet nearly all, perhaps all the plants, in 

 these two similar localities shall be specifically distinct." The 

 same might with equal propriety be said, in a more restricted 

 sense, of the alpine flora of our own and other countries, but 

 not to go beyond our own islands it meets with ample corrobora- 

 tion within themselves. Two places might be found on the 

 mountains of S.W. Ireland and Wales, possessing the same 

 specified conditions, and yet we find that their characteristic 

 alpine flora is totally distinct, the former being allied to that of 

 the West Pyrenees, and the latter, as we have said, to that of 

 Scandinavia. All such difficulties, otherwise insuperable, in 

 understanding the distribution of our Alpine or other floras, are 

 readily explained by the theory which the late Professor Edward 

 Forbes promulgated and illustrated in his essay on this subject 

 appended to the Memoirs of the Geological Survey of Great 

 Britain. In this, he regards our pha^nogamic vegetation as 

 made up of five separate floras,* each of which is intimately 

 related to some distinct continental flora. But it will at once be 

 evident that before our phsenogamic, and let me add also, our 

 cryptogamic vegetation could have been disseminated from these 

 continental centres, a relation very different indeed from the 

 present, must at one time have subsisted between them and our 

 islands. Accordingly Forbes considered the different floras 

 constituting his five types, as outposts, separated by certain 

 Geological changes, such as the rising, subsidence, and dis- 

 location of land, from more extended areas. On this theory, 

 the British Isles were at a former period or periods united hi 



* See Appendix. 



