(151) 
the flora of the wooded portion of the eastern United States, north 
to the transition zone, can be referred to it. 
South of this region and surrounding it on three sides lies the 
coastal plain. Although included with the southeastern center by 
Adams it is distinct from it, and is similarly characterized by a large 
number of endemic forms. From this center species have migrated 
to the northward and westward, following the coastal plain to New 
England and the river valleys to Nebraska and Minnesota. The 
peculiar flora of the swamps of southern Illinois and sontheastern 
Missouri is directly due to the influence of this center, a fact already 
recognized by Bush.* 
n the southwest lies a large, rather vaguely defined center in 
Texas, which may be spoken of asthe Texancenter. It has served 
as the origin of the greater number of species of the prairie prov- 
ince which extends northward from it. Of larger extent and less 
definitely bounded than the southeastern center it has correspond- 
ingly fewer endemic species, but its importance as a distributional 
center is not less. 
The fourth or Ozarkian center was first recognized by Coulter, 
who called attention to the presence there of four endemic genera 
of Umbellifers, and was also mentioned by Bush.{ It includes the 
Ozark region of Missouri, Arkansas and Indian Territory, and ex- 
tends also into Texas. Not only Umbellifers, but other genera and 
species are endemic here, and although of limited extent, the center 
has been of great importance in influencing the flora of the adjacent 
states and traces of its flora are seen even in southern Illinois. 
Corresponding to these distributional centers two principal geo- 
graphic divisions may be recognized among the species of Ver- 
nonieae in the United States, the one southeastern, the other south- 
western. Neither has any standing from a purely morphological 
view, since they are not distinguished by any one set of morpho- 
logical characters. Practically every type of foliage, pubescence, 
involucre, number of flowers or ecological habit found among the 
species in one division is repeated in one or more species of the 
other. But the phytogeographical diversity of the two is evident. 
*Rep. Missouri Bot. Gard. 5 : 140. 
1894. 
+ Geographical distribution of North American Umbelliferae. Proc. Am. 
Assoc. Adv. Sci. 39: 292-298. I 
th. c. 
