I66 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



This great difference in the rapidity with which plants undergo 

 evolutionary development, depending on the growth type to 

 which they conform, is therefore a fundamental consideration in 

 any discussion of endemism. 



Summary 



1. The endemic elements in the floras of the south temperate 

 zone are preponderantly woody; those of the north temperate zone, 

 preponderantly herbaceous. 



2. A distinction should be drawn between "relict" endemics, 

 which are survivors of a once more widely spread flora and there- 

 fore of relatively high antiquity, and "indigenous" endemics, which 

 are of local development and therefore less ancient. 



3. In the endemic floras of Europe and temperate North America 

 almost all tree and shrub genera are relicts. The great majority of 

 endemic herbaceous types, on the other hand, arc apparently of in- 

 digenous origin and have presumably arisen or become widespread 

 since a free exchange of plants between Europe and America was 

 discontinued. 



4. The predominance of herbs among indigenous endemic types 

 is explained as due to the great rapidity with which jjlants be- 

 longing to this growth form may undergo evolutionary develop- 

 ment, owing to the extreme brevity of their life cycle. 



