1919] Hall-Goodspecd: Chrysil 185 



hope for this lies iu the discovery and iraprovement of plants which 

 can be grown in this country and which will be sufficiently productive 

 to warrant their cultivation in competition with imported rubbers. 

 One such species has already been introduced — Mexican Guayule 

 (Parthenium argentatum), now being grown to a limited extent in 

 southern Arizona. There is no assurance, however, th^t this plant 

 can be profitably grown over a sufficiently large area to supply the 

 country's needs in time of ^var, nor are we certain that it is the 

 best one to be used. It is desirable that all promising sorts should 

 be carefully investigated and their possibilities determined. These 

 reasons have led to a broadening of the scope of our inquiry to include 

 a preliminary study of the cultural possibilities of the plants under 

 consideration. 



This extension of the scope of the investigation has emphasized our 

 deficiencies in time and facilities for the satisfactory prosecution of the 

 work. Since it has been carried on thus far as a purely war emergency 

 matter, the aim has been to assemble our information as rapidly as 

 possible, and we have not permitted ourselves to become unduly en- 

 grossed in any phase of the work that seemed to require a long period 

 of study or experimentation. The authors regret this keenly, since it 

 means that the report here presented must be very incomplete ; that 

 many fundamental questions regarding both the scientific and practi- 

 cal aspects of the subject must go unanswered. It seems our duty, 

 however, to place on record such data as we have, including particu- 

 larly such information as will assist those who may interest them- 

 selves in a further search for rubber-bearing plants. Methods of car- 

 rying out the histological examinations and chemical analyses are for 

 the same reason given in detail though they may prove neither novel 

 nor instructive to the trained botanist and chemist. It is hoped that 

 this report will serve as a basis for more intensive researches, either 

 by ourselves or by others, when conditions are more favorable and that 

 it will point the way to special investigations that have to do with the 

 formation and occurrence of rubber in these West American shrubs 

 and its possible utilization by man. 



The preliminary studies here described have been in progress for 

 about two years but the work was carried on only during vacation 

 periods and in such additional time as could be spared from regular 

 university duties. In addition we have profited by the generous assist- 

 ance of numerous co-workers to whom acknowledgment is made below. 



