Gums, Resins, 



196 



(March, 1912. 



The Executive has authority to enter 

 into agreements with the Governments 

 for the States of Para, Mattogrosso, and 

 Amazonas in order to obtain from them 

 a reduction of 50 per cent, upon the 

 export taxes on wild rubber, and a total 

 exemption during the twenty-five years 

 commencing from the promulgation of 

 the present law, from all duties in 

 favour of cultivated rubber produced in 

 these States. The reduction of 50 per 

 cent, mentioned above will be carried 

 into effect by means of annual partial 

 reductions of 10 per cent, until the figure 

 of 50 per cent, is reached. Immediately 

 this agreement has been reached, the 

 Executive will grant the same reduction 

 to rubber exported from the territory of 

 Acre, and the same exemption on cul- 

 tivated rubber. The Government is also 

 authorised to enter into negotiations with 

 the above States with the object of 

 applying to the rubber produced in the 

 territory of the Acre of the same protec- 

 tive measures as will be in force in these 

 States. All dispositions to the contrary 

 are rescinded. 



THE RUBBER-PRODUCING PLANT 

 OF THE MEXICAN DESERTS. 



(From Nature,Ko.2m.i Vol. LXXXVIIL, 

 December 14, 1911.) 



Amongst the botanical collections 

 formed in 1852 by Dr. J. M. Bigelow, 

 whilst attached to the Mexican Boundary 

 Survey, were specimens of a shrub 

 known to the Mexicans as " guayule," 

 afterwards described by Prof, Asa Gray 

 as Parthenium argentatum. No mention, 

 however, was made of its rubber-bearing 

 qualities, It was not until 1876 that 

 public attention was directed to guayule 

 rubber by an exhibit sent to the 

 Centennial Exposition at Philadelphia 

 in that year. The country peon had, it 

 appeared, for long been in the habit of 

 making playing balls and other articles 

 by the " communal mastications " of the 

 bark of this shrub, and it was by that 

 nio.'ios sufficient was obtained for the 

 abave-inenrioned exhibit. Investigation 

 showed that the plant was capable of 

 producing in the neighbourhood of ten 

 per cent, of its weight of dry rubber, 

 and that it grew in vast abundance in 

 the desert country of Northern Mexico. 



This discovery speedily changed the 

 economic value ot these deserts, and set 

 in motion business operations involving 

 millions of capita] based upon the 

 amount of raw material in sight. In 

 1902 chemical and mechanical extraction 

 plants were set up> and guayule rubber, 



though an inferior article containing 

 a high percentage of resinous sub- 

 stance, soon became a very important 

 item in the imports of the United States. 

 At the present day the outlay of 

 American capital in Mexico alone is said 

 to amount to 30,000,000 dollars. 



A good deal has already been written 

 dealing with guayule, but the mono- 

 graph by Prof. P. E. Lloyd is a most 

 welcome addition to special rubber 

 literature. Its contents are the out- 

 come, Prof. Lloyd states in his preface, 

 of an investigation carried out by others 

 and himself at the instigation of certain 

 Mexican rubber companies towards the 

 elucidation of the question of the profit- 

 able cultivation of guayule in the desert 

 with a view to future maintenance of 

 supplies, 



In addition to the physiology of the 

 plant under varied conditions, the main 

 subjects dealt with are questions of 

 climate and soil, seed germination, 

 methods of reproduction, results of crop- 

 ping, environment of the plaut,its rate of 

 growth, methods of extraction, the 

 possibility of maintaining the supply by 

 irrigation, and the effects of this upon 

 the yield of rubber. In the course of 

 the investigation attempts are made to 

 throw light upon many interesting 

 problems in connection with the physio- 

 logy of desert vegetation. 



Much attention has been given to the 

 formation of resin and rubber, and the 

 close connection betweeu the two. There 

 appears to be no tube-like laticiferous 

 system as in other rubber-yielding 

 plants, the rubber being formed ap- 

 parently in the cells of the resin-canals, 

 whilst the resin itself is found only in 

 the canals and not in the cells. 



The guayule shrub is a very slow 

 grower, a fifteen-year-old plant being 

 no more than 15 inches in height, and 

 Prof. Lloyd estimates that existing 

 supplies will, be exhausted in a few 

 years' time. Seed can be germinated 

 and plants easily raised by giving a 

 small amount of shade and subsurface 

 irrigation. On p. 121 the author remarks 

 that " the most fundamental economic 

 question for which an answer will be 

 sought in these pages is that relating 

 to the production of rubber under 

 irrigation." In searching for a reply 

 one has to be content with the statement 

 that " The less the water the thicker the 

 bark (cortex) and vice versa." Irrigated 

 plants naturally grow more vigorously, 

 but produce wood at the expense of 

 cortical tissues, and it is largely the 

 latter from which the rubber is ex- 

 tracted, 



