Apr., 1923] 



GLEASON VERNONIA IN NORTH AMERICA 



195 



of the stem, and new vegetative parts appear only from the perennial base 

 of the plant. In the fifth and last stage, only a few terminal and subtermi- 

 nal heads retain the umbellate arrangement, while from the upper stem 

 axils similar clusters arise, producing a broad, flat-topped or hemispheric 

 cluster with all the heads peduncled. These five stages are shown diagram- 

 matically in figure 2. 



Fig. 2. Modifications of the inflorescence in the bractless Vernoniae of North America 

 A. Stage 1, Vernonia scorpioides, lateral branch with two terminal cymes. B. Stage 2, 

 canescens, lateral portion of the inflorescence. C. Stage 3, havanensis, portion of a terminal 

 inflorescence. D. Stage 4, Karvinskiana, terminal inflorescence, with a few primary branches 

 omitted. E. Stage 5, texana, complete terminal inflorescence. All figures diagrammatic 

 as to position of branches or cymes, but accurate as to character of branching and pro- 

 portion. 



Other evidences of evolution appear within the last two stages, leading 

 to the segregation of several species-groups. 



The five stages are again well correlated with their geographical dis- 

 tribution. The first occurs in South America and is represented in our 

 region by a single species of St. Vincent, V. pallescens Gleason, and by two 

 which extend across the Isthmus of Panama into southern Central America, 

 V. scorpioides (Lam.) Pers. and V. brachiata Benth. The second includes 



