258 Universihj of California Publications in Botany [Vol.7 



Clirysil. The most iiuportaiit spet'ies of Chrysothnninns is C. iiauseu- 

 SHS, under wliidi are rccofi'iiized twenty-two varieties. Twelve of 

 these vai'ieties have been examined and fulilier found in all of 1liem 

 although individual jilants may be devoid of rubber. 



(51 ChnjsothdniHiis nau^eosus is a large shrub, the average weight 

 being from four to six pounds. Tt grows readily from seed and reaelies 

 nuitui'ity in from six to eight years. 



(6) Tlie speeies is widely disti'ibutid in western Xortli America, 

 often iidialnting alkaline flats. 



(7) The largest stands of Chrysil-bearing shi'ub are in ("oloi-ado, 

 Nevada, and T'tali. The ])lants with the highest rubber content are 

 from Nevada and California. The total amount of I'ubber pi-esent 

 in \\ild shrub is estimated at over 300,000,000 iiounds. 



(8) The rubb(^i- oeeurs in the individual cells, and is not a latex- 

 rubber. Its place of occurrence in the i)lant has been rather definitely 

 located. Methods have been developed for its detection by micro- 

 scopical examination as well as by cbemical analysis. A'arious experi- 

 ments indicate that the chemical methods adopted are reasonably 

 accurate ; that great care must be exercised in the preparation of 

 samples for anal^'sis; and that samples do not deteriorate when stored 

 for periods of several months. 



(9) The results of one hundred and eighty chemical analyses and 

 eighty microscopical examinations are tabulated. These indicate an 

 average of 2.83 per cent of rubber in the variety hololeucus, 2.69 per 

 cent in the variety pinifolius, 2.52 per cent in the variety viridulus, 

 1.97 per cent in the variety consimilis, and lower percentages in other 

 varieties. The low-percentage varieties are all comparatively uncom- 

 mon. The highest absolute percentage was found in a ])lant of 

 consimHis collected near Gerlach, Nevada, which analyzed 6.57 ])er cent 

 of pure rubber. The second-highest was a ])lant of viridulus from 

 Benton, California, wiiieh \ielded 5.56 per cent. 



(10) Chrysil occurs in the plant in gi-eatest amount at about the 

 .soil line. In the root it is present in oidy the upper i)art. In young- 

 twigs and leaves it occurs in onl_\- snudl amounts. The richest tissues 

 are found in the cortex and the medullary rays, the former carrying 

 much moi-e tiuin the latter. 



(11) The amount of rubber varies with the botaiueal variety: the 

 best varieties being those which inhabit alkaline soils. 



