1^1^] Hall-Goodspc( (J : Chnjsil 255 



gations, as applied to Chnjsotliamnus. should be along several diverse 

 lines, yet all leading to the same objective. They should include the 

 following : detailed studies of wild plants for the purpose of discov- 

 ering, if possible, better varieties or strains than we now have ; garden 

 experimentation in breeding and selection ; modifications in environ- 

 ment, especially changes in the water relation, and the effect of methods 

 of cultivation ; the effect of varying amounts of alkaline salts on rubber 

 deposition ; and, finally, pruning and other experiments designed to 

 test the possibility of increasing the amount of rubber bearing tissue 

 and also of increasing the percentage in the tissues. 



XIV. CULTURAL REQUIREMENTS 



In case Chrysothamnus is brought under cultivation, its cultural 

 requirements would need to be looked into very closely. At present, 

 our knowledge of these is based upon observations of the wild shrub 

 and upon a limited number of experiments in transplanting and in 

 growing from seed. 



These plants are not exacting as to their climatic requirements. 

 The viriduliis and consimilis forms grow readily from the lowest to the 

 highest limits of the Upper Sonoran Life Zone and exceed these limits 

 slightly in both directions. Expressed in another way, they range from 

 fairly hot interior valleys, where the temperature runs to 110° F. in 

 summer, to over 7000 feet in the mountains where snow falls to a 

 depth of several feet and the temperature drops to — 20° F. in winter. 

 No difficulty has been experienced in growing these varieties in the 

 botanical garden at Berkeley, California, both from seed and from 

 root transplants, but it is doubtful if they will grow here as rapidly 

 or as large as they do under conditions of greater summer heat. Trans- 

 planted seedlings are also growing at the Citrus Experiment Station 

 at Riverside, but they are not at all vigorous. It is not known whether 

 this is due to the very unfavorable climatic conditions that prevailed 

 when thev were set out in the field or to some other factor. Moreover, 

 Riverside is in the Lower Sonoran Life Zone and therefore perhaps too 

 hot in summer for these Upper Sonoran plants. While the exact 

 geographic limits for the cultivation of Chrysothamnus will need to be 

 determined with some accuracy it seems reasonably safe to say that, as 

 far as climate is concerned, it may be grown in any of the larger in- 

 terior valleys of the West except perhaps those of the extreme north 

 and the very hot Lower Sonoran valleys of the extreme south. 



