CHAPTER XII. 



SUMMARY AND CONCLUSION. 



The Present Volume illustrates the Development and Application 

 of a New Law of Dispersal — Past Geographical and Climatic 

 Changes — The Glacial Epoch and its Bearing on the New 

 Law of Dispersal — Effects of the Glacial Epoch on Species — 

 Range Bases — Application of the Law of Dispersal to the 

 Range Contraction and Emigration of British Birds — The 

 Migration of British Birds — Routes of Migration — Conditions 

 of Flight — The Spring and Autumn Aspects of Migration in 

 the British Archipelago — Internal Migrations and Local 

 Movements in the British Area — Irruptic Movements — The 

 New Law of Dispersal — Its Bearing on the Arctic Element in 

 South Temperate Floras — Inter-polar Floras — Impossibility of 

 Emigration of Plants from North to South — Presence of 

 Southern Genera in Europe — The Andes as a Route for the 

 Southern Migration of Plants — The Floras of Mountains in 

 the Torrid Zone during Pre-Glacial Ages — Arctic Floras could 

 never have been Developed in the Polar Regions — Dispersal 

 of Plants North and South from Equatorial Range Bases — 

 Effects of Glacial Epoch on Northern Floras — Absence of 

 many Species from Equatorial Range Bases — The " Retreat " 

 of Plants a Myth — Conditions of Successful Dispersal — The 

 Flora of the Mountains of Asia — Inter-hemisphere Species — 

 Species in Polar and Temperate Zones — The Distribution of 

 Plants in Africa — The Temperate Flora of South Africa — 

 Northern Emigration from Antarctic Centres obviously 

 Erroneous — The Bearing of this New Law of Dispersal on the 

 Absence of Southern Types from the Northern Hemisphere — 

 The Dominant Southern Flora— Its Dispersal from Range 

 Bases South of the Equator — The Problem of Migration and 



