EARLIER INVESTIGATIONS. 9 



carrying as high as 6.5 per cent, while the average is about 2.5 per cent. 

 These figures are for rubber obtained by the acetone-benzene method. 

 In commercial extraction, such as is practiced for guayule, the amount 

 would be increased because of the inclusion of anywhere from 10 to 

 25 per cent of resins and other impurities. The pure product was 

 given the name of chrysil. A total of 300,000,000 pounds was esti- 

 mated to be present in the native plants. Rubber was also found in 

 various amounts in 4 other species of Chrysothamnus and in 10 species 

 of the closely related genus, Haplopappus. Since the prime object 

 was to locate an emergency supply of native rubber, the investigations 

 were not extended to include cultural experiments, although some 

 information is presented that could be used as a basis for such work 

 and as a beginning in breeding and selection. Chrysil is not a latex 

 rubber, but occurs as solid particles in the plant cells, much after the 

 manner of guayule, as is indicated by detailed histological studies, the 

 results of which are presented by these authors. 



Colorado rubber plant. In 1902 and 1903 considerable interest 

 was manifested in a new rubber plant from Colorado and New Mexico, 

 namely, the pinguay (Hymenoxys floribunda utilis) or Colorado rubber 

 plant, as it soon came to be called. This was before the tune of plan- 

 tation rubber and when the crude product from the upper Amazon 

 districts commanded high prices because of the rapidly increasing 

 demand. Small mills were erected in southern Colorado and experi- 

 ments were undertaken in the cultivation of the plant. It was soon 

 learned, however, that profits could not be made by utilizing the wild 

 plants, owing to their small size and scattered growth, and that the 

 plants did not yield enough rubber to make their cultivation profitable. 

 Very little has been published concerning this plant, but there is a 

 note by T. D. A. Cockerell (1903) and another by W. P. Cockerell 

 (1904). The latter states that the roots are said to contain 5 to 12 

 per cent of crude rubber, but apparently this includes a considerable 

 proportion of impurities. Recent analyses have yielded only 3.6 per 

 cent of pure rubber in the root and basal portions of the plant (p. 41). 

 Hillier (1906) expresses the opinion that the product does not compare 

 favorably with many of the lower grades of rubber already on the 

 market. 



Milkweeds (Asclepias spp.) and Indian hemp (Apocynum cannabinum). 

 The first recorded attempt to prepare rubber from any of the plants 

 which grow north of the Mexican boundary was that of William 

 Saunders (1875), who experimented with the common milkweed 

 (Asclepias syriaca = A. cornuti). The investigations were carried on 

 about 1871 at London, Ontario. Saunders reported the preparation of 

 an elastic, vulcanizable gum which he thought could be manufactured 

 at a profit. By allowing the coarse-ground material to ferment for 



