190 AMERICAN JOURNAL OF BOTANY [Vol. 10, 



and the greatest modification is found in V. Schiedeana Less., ranging from 

 Honduras to Vera Cruz, with involucral scales broadly dilated at the tip. 

 The progressive specialization in structure, correlated with increasing dis- 

 tance to the north, is here clearly shown. 



There now follow seven species-groups with 33 species, all West Indian, 

 all clearly related, and all exhibiting a remarkable correlation ,betwee 

 structure and distribution. 



The most primitive of these, from which the other six are directly or 

 indirectly derived, is the Arborescentes, ranging from the Windward Islands 

 to Jamaica. The wide range and primitive structure probably indicate an 

 early arrival in the region. The most primitive species, V. icosantha DC, 

 has stems bearing leaves of normal size to the apex and terminating in a 

 single sessile head. At the base of this head the two primary cymes arise; 

 they are straight, elongate, with prominent internodes, sparingly branched 

 or simple, and bear numerous heads. The chief distinction in the inflo- 

 rescence between it and the Graciles is the regular presence of paired primary 

 cymes. In V. sericea L.C.Rich., of the Virgin Islands and Porto Rico, 

 the cymes are shorter and more frequently branched. V. borinquensis 

 Urban, of Porto Rico, has exceedingly fiexuous, many-headed, freely 

 branched cymes, the branches invariably arising at the base of a head. V. 

 arborescens (L.) Sw., of Jamaica, has numerous frequently congested cymes 

 and reduced bracteal leaves. V. permollis Gleason, of Jamaica, completes 

 the group, with congested cymes and an unusual development of foliar pu- 

 bescence. The general tendency of the group is toward the production of 

 cyme-branches and supernumerary cymes, making a congested inflorescence 

 in which the bracteal leaves are reduced. 



The Longifoliae, a group of three species, is related through V. longi- 

 folia Pers., of the Lesser Antilles,, to V. icosantha. Superficially the two 

 species are much alike, but the inflorescence in the former shows a distinct 

 difference. The primary cymes are short, compact, divergently spreading 

 at an angle of 60-90 , crowded, bearing only 2-5 heads on short internodes 

 with bracteal leaves considerably smaller than the heads. Secondary cymes 

 arise just below the primary in the upper leaf axils. They are essentially 

 leafless for the first 2-5 cm., and then bear toward the summit either the 

 usual crowded heads or a terminal head subtended by two short cymes. 

 This whole inflorescence terminates completely the growth of this portion 

 of the stem, but during the next vegetative season new branches appear 

 from the next lower axils in order, grow out at a divergent angle, soon 

 surpass the old cymes of the previous season, and at the next blooming 

 season bear their cymes in turn. The plant has therefore a method of 

 continuing its vegetative growth beyond one season, and as a result reaches 

 a considerably larger size. V. Shaferi Gleason, of Montserrat, is closely 

 similar, and represents an island endemic. V. albicanlis Pers., of the Virgin 

 Islands and Porto Rico, preserves the same inflorescence but differs in its 

 obtuse or broadly rounded leaves. 



