Apr., 1923] GLEASON — VERNONIA IN NORTH AMERICA I9I 



It is a comparatively short distance across open water to the north of 

 Porto Rico, the home of V. albicaulis, to the southern islands of the Bahamas. 

 In these southernmost islands occurs V. bahamensis Griseb., the most 

 primitive member of the species-group Bahamenses. The fundamental 

 difference between this group and the Longifoliae is again found in the in- 

 florescence. Here the cymes, after the flowering period, continue their 

 e ngation into the vegetative shoots of the next season. Not every cyme 

 necessarily elongates, but there are regularly 2-4 such branches at the apex 

 of each^ year's growth. Toward their base, paired scars mark the location 

 of former heads and bracteal leaves, while above them scars in spiral arrange- 

 ment indicate the former position of foliage leaves. All these Bahaman 

 species are therefore bushy, widely spreading, freely branched shrubs. 

 It is particularly worthy of note that they all have broad obtuse to retuse 

 leaves; that V. bahamensis, the species most nearly resembling V. albi- 

 caulis in leaf form, is the species of the southernmost islands, and that the 

 particular specimen in herbaria which most closely approximates the leaves 

 of the Porto Rican plant in size was collected on South Caicos Island, al- 

 most the extreme southeastern island of the group. V. arbuscula Less, 

 and V. obcordata Gleason occur farther to the northwest in the Bahamas. 

 V. complicate Griseb., of eastern Cuba, differs only in minor characters. 

 It is difficult to imagine a more striking instance of correlation between 

 structure and distribution than is presented by this group in its relation 

 to the Longifoliae. 



The last three species-groups illustrate the following course of develop- 

 ment in the inflorescence: 



1. The cyme is a special branch with reduced bracteal leaves and 

 elongate axis. 



2. The cyme and leafy branches differ merely in position, and the 

 inflorescence is compact. 



3. The cyme becomes the leafy branch at the conclusion of the 

 blooming season, and the inflorescence is compact and reduced. 



The fourth species-group of the seven, the Racemosae, includes five 

 species of Hispaniola and Cuba. They are probably derived from V. 

 sericea of the Arborescentes, which is located near by in Porto Rico; V. 

 racemosa Delp. was considered by Ekman a variety of V. sericea, and, like 

 it, most of the species have leaves pubescent on the lower surface. In this 

 group the two upper primary cymes are short, with only 2-5 heads. Below 

 them, every leaf axil for a considerable distance down the stem produces 

 similar short lateral cymes. The whole makes an elongate subcylindric 

 inflorescence, quite different from the broad, spreading type of the preceding 

 groups. Secondary vegetative branches apparently do not exist. Within 

 the group, evolution is seen in the progressive reduction of the leaf surface, 

 of the cymes, and of the number of flowers in the head. While V. racemosa 

 of Hispaniola has lanceolate leaves, and cymes of 2-5 many-flowered heads, 



