PREFACE VII 
been possible to indicate with unusual precision the range, habitat, 
and period of flowering of most of the species, and for the same reason 
it has been found necessary to describe a considerable number of 
them as new. | 
Part 10 consists of four papers by Dr. S. F. Blake, comprising 
revisions of the genera Acanthospermum, Flourensia, Oyedaea, and 
Tivthona. All these are members of the family Asteraceae, and are 
confined in their distribution to the tropical and subtropical portions 
of North and South America. The study of these groups has been 
based upon the material in the United States National Herbarium 
and the Gray Herbarium, and upon that of several important Euro- 
pean herbaria. 
Part 11, by Prof. Charles V. Piper, is entitled The Identification of 
Berberis aquifolium and Berberis repens. The introduced European 
barberry, B. vulgaris, has long been known as the host of one stage of 
the destructive stem rust of wheat, and the United States Depart- 
ment of Agriculture is now engaged in a campaign to eradicate this 
species in the north-central wheat-producing States in order to con- 
trol destructive epidemics of this rust. A study of other native and 
introduced species of barberry is now in progress to determine 
whether they, also, may serve as hosts of the stem rust or of related 
rusts of cereals and other grasses, or whether they are immune to 
this fungus. The need of an accurate understanding of the species of 
Berberis is of obvious importance. In this paper Professor Piper has 
settled a doubt of long standing regarding the identity of two north- 
western species belonging to the section Odostemon, or Mahonia. 
Part 12, by Mr. Pittier, consists mainly of revisions of critical 
groups of Middle American trees, the more important dealing with 
Machaerium, Pithecollobium, and Lucuma, of the families Fabaceae, 
Mimosaceae, and Sapotaceae. There are included also a key to the 
Mexican and Middle American species of Vitex, with descriptions of 
several new species, and a revision of the cucurbitaceous genus 
Calycophysum. Descriptions of three new species of Zanthorylum 
from Panama are contributed by Mr. Percy Wilson, of the New York 
Botanical Garden. 
Part 13 consists of three papers by Dr. S. F. Blake. In the first, 
entitled Revision of the American Species of Rinorea, 39 species are 
recognized. znorea is a genus of the family Violaceae, consisting 
of trees or shrubs with inconspicuous flowers, and is well represented 
in the American tropics. The second paper, entitled New Plants 
from Venezuela, contains descriptions of 34 new species of flowering 
plants and of a single new moss, the latter contributed by Mr. R. S. 
Williams. The third paper describes Hemibaccharis, a new genus 
of Baccharidinae, consisting of 15 species, 6 of which are new. This 
