



25 6 MISSOURI BOTANICAL GARDEN. 



The work on the gross structure is being supplemented by 

 a histological investigation of the anthers of the forms in 

 question, and some hundreds of microscopical slides have 

 been prepared and examined. Because of the great variety 

 and in many cases complexity of structure this promises 

 to be one of the most important phases of the work. 



It has been shown that apically dehiscent forms for the 

 most part fall into well defined categories exhibiting a 

 striking uniformity of structure in genera or species from 

 widely separated families. Structural parallelism in a series 

 of floral forms assembled from phylogonetieally widely sep- 

 arated groups necessarily implies the anomalous structure 

 of many of the forms in the groups to which they syste- 

 matically belong, among the forms to which they are genet- 

 ically related. Of the real process by which this paral- 

 lelism has been evolved I do not yet care to say anything. 

 Many of the conclusions drawn from ecological studies are 

 of little value because of the inadequacy of the data con- 

 sidered. Comparative researches attain their fullest value 

 only when based on the largest series of material. At the 

 present time, it seems to me, one of the most important 

 things is to determine in how far floral organizations do 

 really fall into well defined groups and in how far the 

 structural characteristics of such groups may be regarded 

 as adaptations. The first of these problems may°be an 

 herbarium and library investigation while the solution of 

 the second is to be approached only by field studios. 



Of the third and last problem little need be said. The 

 tables presented show clearly that the apically dehiscent 

 genera and species are not only much more abundant 

 numerically in tropical America, Australia and the Indian 

 region, but also that they form there a larger proportional 

 constituent of the flora than they do in other regions. ThL 

 distribution seems to depend in large measure upon the 

 relative abundance of the Apidae in the several divisions. 



