1919] Hall-Goodspced: Chnjsil 257 



Similarly, large suitable areas now partly covered with Rabbit-brush 

 are located in Fish Lake Valley, Big Smoky Valley, Walker River 

 Valley, near Mono Lake, and elsewhere in Nevada and eastern Cali- 

 fornia. In Utah and in Colorado (especially the San Luis Valley) 

 there are extensive tracts of practically waste land where the varieties 

 consimilis and pinifolius are abundant. Finally, the Sacramento and 

 San Joaquin valleys of California include large acreages of practically 

 unused alkali lands where, unless the summer heat is too great, 

 Chrysothamnns could probably be grown. 



Chrysothamnus is thus seen to be a hardy plant capable of growing 

 under a considerable range of climatic and soil conditions. It is ap- 

 parently best suited to the alkaline plains of the Great Basin, especially 

 if the soil is somewhat sandy. This fact, together with certain other 

 practical considerations, would indicate that if the plants are brought 

 under cultivation the first plantations should be located in these in- 

 terior districts, some of the most promising of which are those indicated 

 above. Zonal position should be taken into account since it seems un- 

 likely that the best sorts of Rabbit-brush can be grown to advantage 

 outside of the Upper Sonoran Life Zone. 



XV. SUMMARY 



(1) It was the object of this investigation to discover a supply 

 of rubber in native North American shrubs which might be used in 

 time of war, thus rendering the nation to some extent independent 

 of overseas importations of this substance. The studies were extended 

 to include a preliminary inquiry into the possibility of bringing the 

 plants under cultivation. Chrysothamnus or Rabbit-brush, was the 

 genus of shrubs especially studied. 



(2) The work was fostered by the Committee on Scientific Research 

 of the State Council of Defense for California and by the University 

 of California. It was furthered through the aid of a considerable 

 number of correspondents. 



(3) Chrysil is the name adopted for the particular kind of rubber 

 found in Chrysothamnus nmiseosus. It is a rubber of high grade and 

 vulcanizes without difficult}'. 



(4) Rubber was found in two closely related genera of shrubs, 

 namely, Chrysothamnus and Haplopappus. Onh- the former yields 



