VARIABILITY IN FLOWER-NUMBER IN 

 VERNONIA MISSURICA RAF. 



DR. H. A. GLEASON 

 New York Botaxical Garden 



In studying the species of Vernonia in the western 

 states, the writer was impressed as early as 1903 by the 

 constancy w^th which the number of flowers in each head 

 of certain species agrees with the numbers of the Fibo- 

 nacci series. This appeared at the time to be particularly 

 true of Vernonia fasciculata, which normally presents 18 

 to 21 flowers. Extending his studies later to the species 

 of tropical America, he found a still closer agreement 

 with the Fibonacci series in the species with fewer-flow- 

 ered heads, wkere the numbers 8 and 13 are repeated 

 with little or no variation in several species. Inspired 

 by the more recent studies of Stout and Boas,^ who re- 

 ported a steady seasonal decrease in flower-number in 

 the heads of Cichorium Infybus, he again examined in 

 1918 a series of specimens' of Vernonia missurica, the 

 only species native in the vicinity of Ann Arbor, Mich., 

 and made careful determinations of the number of flowers 

 in every head of several plants, chosen from different 

 localities and habitats. The results of these studies are 

 presented here. 



In the western part of its range, from Kansas to Illi- 

 nois, Vernonia missurica is essentially a prairie species 

 and is seldom or never found in woods or swamps. In 

 Indiana it is excessively common on rolling hills in clay 

 soil, preferring land formerly wooded but now used for 

 pasture, where it is apparently avoided by live-stock. 

 In the extreme cnstci-n cihI of its t-;uiu'p. in southeastern 



