1^19] Hull-G Godspeed: Chnjsil 243 



for teretifolius, globules only being found both in younger and older 

 elements. The cross section of a leaf of a plant grown in the 

 University of California Botanical Garden is shown in figure 6. The 

 dark stained rubber globules in the palisade cells are conspicuous. 

 Lloyd^^" reports that a single large globule of rubber was character- 

 istic of each palisade cell in certain portions of the leaf in Guayule. 

 A corresponding condition holds for Chrysothaninus although in some 

 instances it appears that more than one globule may occur in a single 

 palisade cell. Various problems dealing with the origin of rubber and 

 its distribution in younger tissues have been investigated in a prelim- 

 inary way, at least. The results of these studies will be published in 

 the near future as the fourth paper of the present series. 



XI. FACTORS INFLUENCING RUBBER CONTENT 



a. VAEIATIOX WITH THE BOTANICAL VARIETY 



The results of our studies, more particularly the chemical and 

 microscopical examinations, indicate that rubber is present in only a 

 few of the major species of Chrysothamnns. The species examined 

 and in which it was not found with certainty are : C. Greenei, C. 

 Howardi, C. nevadensis, C. Parryi, C. hiimilis, C. piiherulus, and 

 C. viscidiflorus. In C. liuifolius, which is perhaps only a varietj^ of 

 viscidiflorus, it was found to the extent of 1 per cent in one sample 

 but was lacking- in another. The species of Chrysothamnns now 

 known to yield rubber are (\ nauseosns, ('. inrhinatus, ('. trretifolins. 

 and C paniculafus. The last three of these are discussed elsewhere 

 since they are of minor importance and the product is not Chrysil.^" 



Coming now to a consideration of C. nanseosns, we find that this 

 variable and widespread species breaks up into about twenty-two 

 varieties. It may be predicted with reasonable certainty that Chrysil 

 will be found in all of these twenty-two forms. This statement is 

 based upon the fact that of the thirteen thus far investigated every 

 one has yielded a greater or less amount of this substance. It might 

 be assumed, a priori, that certain of these botanical varieties would 

 carry a consistently higher percentage than others. This assumption 

 is borne out to some extent by the analyses, as is indicated in thi' 

 following summary of the analytical tables published in detail on 

 pages 226 to 233. 



18" L.C., p. 184. 

 i:i See pp. 265-268. 



