Blake — A Revision of the Genus Viguiera 29 
or less callous-mucronulate phyllaries with rather strongly ribbed 
base and loose herbaceous apex. In the subgenus Yerbalesia (t. 
2. f. 34), finally, the involucral characters are much as in some 
species of the series Aureae already described. 
This summary of involucral conditions in the genus has, it is 
hoped, served to bring out the fact that in two distinct areas — 
Mexico, with Central America and the United States, on the one 
hand, and extra-tropical South America on the other — two groups 
of species, certainly separated for a long period, have developed in 
the evolution of their involucres very similar and often parallel sets 
of tendencies, although the genetic relationship between any pair 
of assimilated groups of the two areas is, so far as all the other 
characters of the plants indicate, no closer than that between much 
more widely different groups of the two regions. Examples of this 
parallelism are shown by the V. cordifolia group of Mexico and V. 
Szyszylowiczit of Peru, the series Dentatae of Mexico and V. 
australis of Peru, and particularly by the series Bracteatae of Brazil 
and Paraguay and the section Leighia of Mexico and Lower Cali- 
fornia. 
Receptacle and Pales. The receptacle of Viguiera varies from 
flattish or slightly convex to low-conical without distinct line of 
demarcation, reaching its highest degree of convexity in V. Porteri. 
The importance of the form of the receptacle was exaggerated by 
the early botanists, especially by DeCandolle, whose conclusions 
often based on imperfect or unripe material have required much 
correction. Thus his primary division of Viguiera in 1836 was 
into “§ 1. Receptaculo acute vel obtuse conico,”’ including six 
species, and “ § 2. Receptaculo planiusculo,”’ with seven. 
of the species of his second group, however (V. brevipes, V. laza, 
V. oppositipes), with all six of his first, are reducible to one species, 
V. dentata (Cav.) Spreng.; nor is the conical character of the re- 
ceptacle in this plant really very pronounced, as compared with 
average species of the genus. On the whole, the apparently slight 
significance of variations in the shape of the receptacles in this 
genus, the difficulty of describing intelligibly their often slight com- 
parative differences, and the impossibility of discovering the 
character of the receptacle, in many cases, without serious injury 
to the specimen, have led me to neglect this feature almost en- 
tirely. 
