VI PREFACE. 



new and little known species of Asclepiadaceae and Cucurbitaceao, 

 keys to the species of several genera, and the characterization of two 

 new genera, Frantzia and Polakowskia, from Costa Rica. 



In part 5 Mr. 0. F. Cook, of the Department of Agriculture, dis- 

 cusses the relationship of the ivory palms, a matter which has long 

 been the subject of doubt and indecision among botanists. In his 

 various expeditions to tropical America in the interest of agriculture, 

 Mr. Cook has been able to make extensive observations on the various 

 groups of palms, including Manicaria, apparently the nearest relative 

 of the ivory palms. This has given him important first-hand infor- 

 mation bearing on the question of family relationship. 



Part 6 consists of two papers by Paul C. Standley, assistant curator 

 in the Division of Plants, which are designed to assist students of the 

 taxonomy and distribution, and to some extent of the ecology, of the 

 New Mexican flora. The first contains an annotated list of all those 

 plants that have their type localities in New Mexico. So far as can 

 be learned no list of this kind has ever been prepared before for any 

 State or Territory, in spite of the obvious advantages which such a 

 work offers. It is interesting to learn that from New Mexico alone 

 almost 700 new plants have been described. Accompanying the 

 list of species is a list of localities with the names of the species 

 described from each; and in order to facilitate the finding of the 

 localities, a map of New Mexico has been prepared, upon which all 

 the type stations have been conspicuously marked. As an aid in 

 the study of the collections made by some of the earlier botanical 

 explorers of this region notes regarding their itineraries have been 

 collected and tabulated. It has been found necessary in preparing 

 the list of species to form several new binomials ; these will be found 

 listed at the end of the paper. The bibliography which forms the 

 second of the papers is intended to be a complete index to the litera- 

 ture of New Mexican botany. 



In part 7, consisting of a paper by Mr. Henry Pittier, an attempt 

 has been made to describe systematically the various American forms 

 of Castilla, along lines indicated in a former paper by Mr. O. F. Cook. 

 Investigations made by the United States Department of Agriculture 

 during the last 10 years have shown that the Central American 

 rubber tree is not, as generally accepted, a homogeneous species, but 

 that it consists of several well characterized forms which differ 

 materially in their geographic distribution and climatic correlation. 

 Hitherto rubber planters have made no distinction between these 

 forms, and many of the unsuccessful attempts at the cultivation of 

 Castilla as a rubber-producing tree may be traced to the want of 

 discrimination in the choice of the form from which the seeds were 

 taken. Although Mr. Pittier has brought to this work a long practical 

 experience in the field, and has had an abundant supply of material 



