6 PLANT GEOGRAPHY 



for dispersal, the barriers to migration, and how they 

 have been surmounted. Thirdly, the floristic regions 

 of the globe will be briefly described; and, lastly, the 

 chief ecological groups will be discussed. Some elemen- 

 tary knowledge of botany and geography must be 

 assumed; and it is obvious that, within the compass 

 of a little book like the present, no part of so wide 

 a subject can well be treated at all completely. The 

 whole book is but an introduction ; but the author hopes 

 soon to issue a more comprehensive work in which each 

 division of the science can be dealt with more fully. 

 More space has intentionally been devoted to the causes 

 than to the results of distribution. 



