THE DEHISCENCE OF ANTHERS BY APICAL PORES. 243 



relative number of genera or even species represented in a 

 region as indicative of the ecological conditions prevailing 



there. Only 



observations 



the fauna and 



flora will yield the exact data requisite for a satisfactory 

 solution of the problem of the mutual interdependence of 

 the distribution of floral structures and the organic envi- 

 ronment to which they are adapted. Even these field 

 studies cannot lay before us the past history of the species 

 or structures in question and our knowledge must always 

 lack the exactness of some other phases of biological inves- 

 tigation. These limitations notwithstanding, we should 

 attempt to bring our knowledge to the greatest exactness 

 possible. The broad outlines of a problem are often 

 obscured for the naturalist in the field by the details of his 

 observations and must be formulated by the worker in the 



herbarium and library. 



I have been unwilling to forego an attempt at a compari- 

 son of the several regions by species. The difficulties in 

 the way of such an undertaking are known only to those 

 who have made a similar attempt. In the very beginning 

 of the present study, it became evident that a comparison 

 of the regions by per cents of the apically dehiscent species 

 in the flora was quite out of the question, and even a com- 

 parison by genera, rough and unsatisfactory as it is, has 

 required many months more than was originally antici- 

 pated. 



The accompanying table, D, is a summary of the number 



of species of the Solanum-Cassia type occurring in each 

 region and the per cent of the total number of apically 

 dehiscent species of this type known, 1,827. 





