VI PREFACE 
species are already in successful cultivation. One of the most striking 
of the Rocky Mountain species, Aquilegia caerulea, has been adopted 
by the State of Colorado as its floral emblem. 
Part 5, by Mr. G. P. Van Eseltine, of the Bureau of Plant Industry, 
United States Department of Agriculture, deals with the southeastern 
species of Selaginella allied to S. rupestris. Notwithstanding the 
attention previously given this group, it is apparent that the species 
are imperfectly delimited in current treatments and are in need of 
critical revision. A more satisfactory treatment is now possible 
through the study of additional material which has accumulated as 
a result of recent botanical exploration. 
Part 6, which is the third of a series upon tropical American 
phanerogams by Mr. Standley, consists chiefly of descriptions of new 
species of shrubs and trees, largely Leguminosae from Mexico, and of 
Rubiaceae from several regions of tropical North America. The 
former are preliminary to the proposed publication of a systematic 
work upon the woody plants of Mexico, upon which Mr. Standley is 
engaged. There is included a synopsis of the Mexican and Central 
American species of Erythrina, a group whose species have long been 
in confusion. 
Part 7 consists of two papers by Dr. 5S. F. Blake, of the Bureau of 
Plant Industry, United States Department of Agriculture. The 
first, entitled The Genus Homalium in America, is a revision of a 
difficult genus of the family Flacourtiaceae, the species of which are 
valued as timber trees. The number of species recognized is 19, 
11 of which are described as new. The second paper, entitled New 
South American Spermatophytes Collected by H. M. Curran, de- 
scribes 13 new species, chiefly shrubs or trees, from recent collections 
in the State of Bahia, Brazil, and the Department of Bolivar, Colom- 
bia. These collections were made by Mr. Curran in connection with 
a general survey of the timber resources of the regions mentioned. 
Part 8, by Prof. Alexander W. Evans, of Yale University, deals 
with the North American representatives of Asterella, a difficult 
group of liverworts concerning whose classification there has been no 
general agreement. The present study fixes the type of the genus, 
discusses the general morphology of the group, describes the North 
American species, three of which are new, and contains a key for 
their identification. 
Part 9, by Dr. Francis W. Pennell, consists of an account of several 
genera of the family Scrophulariaceae as represented in the central 
Rocky Mountain States. The greater part of. the paper relates to the 
genus Pentstemon, a large and difficult group containing many species 
which are among the most characteristic and attractive members of 
the Rocky Mountain flora. Because of the intensive character of the 
study, which is based largely on field work by; the¥author, it has 
