THE DEHISCENCE OF ANTHERS BY APICAL PORES. 239 





It is evidently of great importance to ascertain just what 

 per cent of the total number of plants known is to be 

 found in each of these regions. The per cent of apically 

 dehiscent forms occurring there can then be compared 

 with this and it may be readily seen whether it is relatively 

 0-reater or less than in other regions. A difference in the 



number of genera with a given floral habit in two floras 

 which are being compared has little significance if the 

 relative number of genera in the two floras varies in the 

 same ratio. There must be some basis for comparison ; 

 the general conditions of life permit of a greater differ- 

 entiation in some regions than in others of the same area 



must 



and the extent of this differentiation 



serve as a basis for comparisons of the development of 



particular elements. 



Bein°r unable to find any suitable statement of the rela- 



tive richness of the floras of different areas it became 

 necessary to tabulate them especially for the present pur- 

 pose. A comparison by species would probably be the 

 most satisfactory, but it soon became evident that this 

 presented too many difficulties. I therefore decided to 

 tabulate the genera only and to take the data for this pur- 

 pose from Die Natiirlichen Pflanzenfamilien. 



In the preparation of these tabulations the 8,541 genera 

 of flowering plants were first set down in order followed 

 by the numbers of the regions in which they occur. These 



summ 



endemic and occurring in each region being indicated. 



I present in Table A a summary of the distribution of all 

 of the flowering plants arranged according to regions. In 

 the first column is given the number of the several re- 

 gions, in the second the number of endemic genera and the 

 per cent which this is of the total number of genera of 

 flowering plants, in the third column the number of genera 

 occurring but not endemic, and in the fourth column the 



' 



