EARLIER INVESTIGATIONS. 7 



author are that the culture of Castillo, has passed the experimental 

 stage, but he emphasizes the fact that the regions in Mexico and Central 

 America well adapted to its culture are much more limited than 

 generally supposed. With no attempt to discourage rubber cultiva- 

 tion in those districts, he nevertheless urges caution in making invest- 

 ments. The rubber, which is carried by a latex obtained by the tap- 

 ping process, is scarcely inferior to Para rubber and is obtained 

 in some quantity from native trees in Central America. 



Other Mexican latex plants. Mexico is a very promising field for 

 exploration with the object of discovering plants capable of yielding 

 rubber in commercial quantities, both from the native growth and 

 from plantations established for this purpose. This was the conviction 

 of the late Dr. Pehr Olsson-Seffer, who, more than anyone else, had 

 looked into the matter as an experienced student of rubber plants. 

 In fact, Olsson-Seffer was preparing to take advantage of this knowl- 

 edge when political disturbances in Mexico, and finally his own death 

 in connection with one of these, put a stop to his plans. The plants 

 which he considered as of greatest value are species of Jatropha, 

 Plumeria, and Euphorbia which have, in addition to their qualities 

 as rubber producers, the very desirable ability to reproduce from the 

 base when the tops are removed, thus affording a perennial supply 

 and avoiding the great expense of tapping by hand. The results of 

 Olsson-Seffer's studies have not been published in detail, although 

 some reference has been made to them by Dunstan (1910) in an article 

 in which it is said that some species of Plumeria yield a latex averaging 

 14 to 16 per cent and sometimes with as much as 24 per cent of rubber, 

 while the latex of Euphorbia calyculata yields 21 per cent of rubber of 

 good quality. 



A Mexican plant which has received some attention as a source of 

 rubber is the palo amarillo (Euphorbia fulva Stapf , E. elastica Alta- 

 mirano and Rose, not Jumelle). The best account of this species has 

 been given by Rusby (1909), who states that it is a tree of the sub- 

 tropical region, and especially of the hilly country, where the western 

 edge of the Mexican table-land breaks down into the coastal slope, 

 at an altitude mostly of 5,000 -to 7,000 feet. It belongs principally 

 to the States of Michoacan, Guanajuato, and Jalisco. The latex is 

 obtained by tapping and that from the stems carries 7.3 to 15.7 per cent 

 of caoutchouc. The rubber is about equal in value to that of guayule, 

 but the amount collected has been so small that it has not entered into 

 commerce to any appreciable extent. The chief interest in this plant 

 lies in its possibilities if properly developed. It is very easily propa- 

 gated by cuttings and full-sized trees are thus obtained in 5 to 7 years. 



Other Mexican species mentioned by Dunstan (1910) as containing 

 small amounts of rubber are Jatropha urens, Pedilanthus tomentellus, 

 and P. pringlei. 



