PREFACE. 
Of the seven parts composing volume 18 of the Contributions, tho 
first is by Mr. W. E. Safford, of the Bureau of Plant Industry, United 
States Department of Agriculture. It represents an extension of his 
work on the family Annonaceae. In various preliminary papers 
Mr. Safford has proposed several new sections of the genus Annona 
and has described many of the tropical American species. The 
present treatment is more comprehensive, embracing a synoptical 
view of the genus by natural groups and sections, with descriptions of 
additional new or inadequately known species. There are given, 
also, descriptions of two closely allied new genera, Fusaea and Gean- 
themum, and critical notes upon Rollinia, Duguetia, and Raimondia. 
This last genus, recently founded upon a single species, is found prop- 
erly to include also a Colombian plant, described long ago by Hum- 
boldt, Bonpland, and Kunth as Anona quinduensis. 
The second paper, by Mr. Henry Pittier, also of the Bureau of Plant 
Industry, United States Department of Agriculture, is in continua- 
tion of a series begun by him several years ago in the Contributions, 
dealing principally with Colombian and Central American plants 
which are of economic value. Besides descriptions of two new species 
of Brosimum and Spondias there are included further notes upon the 
difficult genus Sapium and a discussion of the nomenclature of the 
sapote and sapodilla, two important tropical American fruit trees 
whose taxonomic history is exceedingly involved. 
The third part consists of a second installment of studies by Mr. Paul 
C. Standley, of the United States National Herbarium, upon the 
flowering plants of tropical America. The new species described 
and the changes of nomenclature proposed are largely the result of 
work upon certain groups, chiefly Rubiaceae, Malvaceae, and Legu- 
minosae, as represented in the extensive collections obtained recently 
in Panama during the progress of the Smithsonian Biological Survey 
of the Panama Canal Zone. A large part of the paper consists of 
descriptions and nomenclatorial changes in the Amaranthaceae and 
Allioniaceae incidental to monographic work upon these families. 
Two new genera are proposed in the Malvaceae. 
Part 4 is the fifth paper of Mr. Pittier’s series mentioned above. In 
this part are discussed various trees and shrubs of Central America 
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