398 CARNEGIE INSTITUTION OF WASHINGTON. 



Taxonomy of Haplopappus, by H. M. Hall. 



This genus of the composites lias been chosen for taxonomic study 

 because of its complexity and because it serves to illustrate the phylo- 

 genetic treatment of the segregates of a genus, especially where these 

 are of very unequal value. Haplopappus is about equally well repre- 

 sented in North America and in western South America, comprising 

 about 200 species, although several times this number have been pro- 

 posed. Previous workers have assembled the species and minor f onus 

 in a variety of ways, and many generic segregates have been made 

 to accommodate them. The present study is an attempt to organize 

 the large number of forms in conformity with their evolutionary 

 development and to present a natural and usable classification. Dur- 

 ing the year all of the material in several of the larger herbaria has 

 been studied, and photographs secured of the more critical specimens. 

 Field work has been prosecuted in the northern Rocky Mountains 

 and the Great Basin, and photographs, field notes, and statistical 

 material have been assembled for detailed study. 



Rubber Platits, by H. M. Hall ajid Frances Long. 



Studies have been continued on the rubber-content of native North 

 American rubber plants, as also upon the life-histories of a few of the 

 more promising species. The results of 4 years' work have been as- 

 sembled and published (Carnegie Inst. Wash. Pub. 313, 1921). In 

 this paper a report is given of the examination of 137 species of plants, 

 of which 74 were found to contain rubber, though most of them 

 showed but small amounts. Ten species are considered worthy of 

 further study, and two of these, Asclepias subulata and A. sulHvanti, 

 are of especial promise. The latter carries 1.2 to 8.1 per cent of rubber 

 in its leaves, while the former, which is a nearly leafless desert peren- 

 nial, carries 2.0 to 5.2 per cent in the stems. In addition, this desert 

 milkweed yields 43 per cent of fiber, equivalent to 28.5 per cent of 

 bleached paper. The previous extraction of the rubber favors rather 

 than hinders the manufacture of paper-pulp. The plants grow readily 

 in desert soil without irrigation, and since the stems can be harvested 

 without destroying the root, a large annual tonnage of shrub per acre 

 may be predicted under agricultural practice. Actual commercial 

 planting, however, must be preceded by extensive experiments in 

 manipulation and especially in breeding, ^^ith a view to increasing 

 the amount of rubber in the plants. 



Cooperative arrangements have been entered into \\'ith plant- 

 breeders, and with rubber and fiber experts, and the investigation is 

 being continued along the following lines: (1) Further field explora- 

 tion to discover better rubber-producing species and strains; (2) experi- 

 ments in breeding and selection ; (3) ecologic experiments on the effect 

 of different habitats, pruning, and various agricultural practices; 



