200 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
tendency is apparent, except in the one feature of inflorescence. In every 
case it is found that species structurally aberrant from the general type 
Fig. 3. Migration and evolution of the bractless Vernoniae of North 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 
