2 OUTLINE OF PLANT GEOGRAPHY 



The main problem of the student of plant geography is to dis- 

 cover, if possible, the explanation of the diverse floras of the dif- 

 ferent parts of the earth, as well as resemblances which occur 

 in widely sundered lands. 



Could we know the whole history of the evolution of the plant 

 kingdom, this problem would be simple enough; but our knowledge 

 of the vegetation of the earliest geological periods is almost nil; 

 and it is not until a comparatively late period that we have any 

 certain evidences of the nature of the vegetation. 



As we study such relics of the ancient floras as have come to 

 us in a fossil state, we realize that the distribution of land and 

 water upon the earth's surface has undergone many and extensive 

 changes. Lands once connected are now widely sundered, and 

 regions now united were separated by great expanses of ocean. 

 Continents have sunk beneath the ocean, and lofty mountain 

 chains have emerged from the ancient seas. 



These changes in the distribution of land and water have doubt- 

 less had much to do with the fluctuations of climate indicated by 

 a study of the ancient rocks and fossils. These reveal the presence 

 of luxuriant vegetation in regions now quite impossible for its 

 existence. Within a few degrees of the poles, in both hemispheres, 

 fossil plants have been found which must have grown in a climate 

 at least temperate in character. 



A study of these evident changes in climate and topography 

 and the fossils that have been discovered, have thrown much 

 light on many facts in the present distribution of plants, that 

 otherwise would be quite incomprehensible. 



While the fossil record is very incomplete, nevertheless it has 

 greatly helped in our understanding of the relations existing be- 

 tween the vegetation of regions now widely separated but which 

 we know were once connected. 



However, much more must be done in the study of the 

 fossil plants of many parts of the world before we shall be in 

 a position to solve some of the most difficult questions of dis- 

 tribution which remain to be answered. It is to be hoped that 

 in course of time with our increasing knowledge of the ancient 

 floras of the more remote parts of the world, that we may 

 solve some of the many puzzles in the distribution of existing 

 plants. 



