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AMERICAN JOURNAL OF BOTANY 
[Vol. 10, 
several species of northwestern South America, some of which extend into 
Central America also, and several others ranging as far north as southern 
Mexico. Species of the third stage have crossed the narrow channel from 
Yucatan and are now limited to western Cuba; the fourth is confined to 
Mexico, and the fifth has four species in northern Mexico and 31 in the 
United States and the Bahamas. 
The species-group Stellares, representing the second stage, includes the 
commonest species of the mountains of Colombia, Central America, and 
southern Mexico. The Colombian species V. canescens H.B.K. and V. 
mollis H.B.K. retain the primitive character of acuminate involucral 
scales; the former also extends north into Mexico, and the latter is doubt¬ 
fully admitted into the North American flora. Of the remaining five with 
acute to rounded scales, V. patens H.B.K. occurs in both continents, while 
the others are strictly North American. The most advanced morphologi¬ 
cally is V. morelana Gleason, which alone does not occur south of Mexico. 
The third stage includes the species-group Menthaefoliae, undoubtedly 
closely related to the Stellares, but now isolated in western Cuba and the 
Isle of Pines, except for a few specimens from central and eastern Cuba as 
well, where they may have been recently introduced. 
The fourth stage includes three well-marked species-groups, which 
are nevertheless closely related. The Umbelliformes include 9 species, 
mostly quite closely related and in some cases separated with difficulty. 
The simplest species (and the commonest in herbaria) have small heads, 
with short involucres and seldom more than 15 flowers; the more advanced 
have larger heads and taller involucres. One of these, V. Conzattii Robin¬ 
son, with its abruptly rounded and mucronate involucral scales, marks a 
transition to the group Mexicanae, with three species in the higher moun¬ 
tains of southern Mexico. Here the scales are extraordinarily specialized, 
being 3-8 mm. wide, loosely spreading, at least at the tip, and prominently 
reticulately veined. The two closely related species of the Alamanianae 
have also large scales but lack the reticulate venation. The general evolu¬ 
tionary tendency of the series is apparently toward large heads and special¬ 
ized scales, and this is correlated geographically with an ascent to higher 
levels in the mountains. 
Passing now to the 35 species of the fifth stage of evolution, as shown 
by the inflorescence, we find the most primitive members in the Texanae, 
a group of four species, three in northern Mexico and one in Texas. Since 
the inflorescence has already passed to the paniculate stage, equally char¬ 
acteristic of the other species of the United States, evidence for the primitive 
character of the group must be sought in other characters. The leaves in 
all four species are more or less pitted beneath and the outer pappus bristles 
are poorly differentiated from the inner in width, both of which features 
occur also in the Umbelliformes. The most important primitive character, 
however, lies in the involucre, and has not been mentioned before because 
