200 



AMERICAN JOURNAL OF BOTAXV 



[Voi. 10, 



tendency is apparent, except in the one feature of inflorescence. In every 

 case it is found that species structurally aberrant from the general type 



CAM ADA 



Prairie 

 Region 



Fasc iculatae 



Central 



— ^ Forests 



Interiores 



Altissimae 



— ^ Ozark Mta. 

 Lottermanni ^ 



Alleghenian Region 



Coastal Plain 



Advanced Involuc re 





Llndheimer 



ianae 



Primitive Involucjre 

 Angustifollac \ 



UNITED 



STATES 



\ Gigantea 



MEXICO 



Bolleana 



t 



Inflorescence Stage ^ 



CUBA 



Menthaefoliae 



CENTRAL AMERICA 



Inflorescence Stage 1 



St .VINCENT 



pallascens 



SOUTH AMERICA I Soorpol des 



FlG. 3. .Migration and evolution of the bractless \'ernoniae of Xorth America. Solid 

 lines show distribution by their location, migration by the direction of the arrow. Dotted 

 lines show probable connection between species-group. 



occupy outlying ranges or peculiar habitats. The evolution in structure 

 may be summarized as follows: 



1. From elongate cymes to short, compact, freely branching cymes 

 or capitate clusters. 



2. From small, acute or acuminate involucral scales to broad, blunt, 

 or veiny scales, or to narrow, prolonged, or filiform scales. 



3. From a medium number (13-21) of flowers in each head to a large 

 number (55-89, or even more), or to a reduced number (as low as 5). 



4. From lanceolate, acuminate leaves to linear, 1 -nerved, or revolute 

 leaves, or to blunt, broad, rigid or coriaceous leaves. 



In the leafy-bracted forms, comprising 57 species, there is a general 



