192 University of Calif ornia Puhlications in Botany [Vol. 7 



elusive of the twigs, and shrubs weighing twenty to forty pounds are 

 not rare. For purposes of estimate, however, much smaller figures 

 must be used. This is partly because the plants reach the maximum 

 size only under favorable conditions and partly because they are fre- 

 quently burned or cut off near the base, after which new stems shoot 

 up only to be again destroyed before reaching maturity. After weigh- 

 ing numerous samples and after making thousands of estimates in the 

 field tlie authors believe six pounds to be a fair average weight of the 

 woody portions of the vindulus variety as it grows in eastern Califor- 

 nia and western Nevada. This includes the root to a depth of only 

 four inches (10 cm.). This estimate does not include young seedlings 

 nor young second growth. 



On a similar basis it is estimated that individuals of consimilis, the 

 common variety in northeastern California, Nevada, and western 

 Utali, will average five pounds, while variety pinifolius of Utah, 

 southern Colorado, etc., will average four or five pounds. 



The rubber producing kinds of Rabbit-brush all grow from deep 

 taproots which have normally but few main laterals. There are usually 

 several trunks from a single base and these are clothed in age wuth 

 loose, fibrous brown bark which peels off in strips. Straight clear 

 stems are the exception. The branches are usually numerous; they 

 often exhibit many distortions and irregularities and are of unequal 

 size. This has a bearing upon the possibility of decortication by ma- 

 chinery, a point of considerable practical importance. The rubber is 

 carried chiefly in the inner bark and in the very outermost portion of 

 the wood, so that decortication would greatly reduce the bulk and 

 weight of the material to be extracted. The irregularities just men- 

 tioned would presumably render decortication by machinery imprac- 

 ticable as far as wild shrub is concerned. If the plants are brought 

 under cultivation they would be more regular and uniform in their 

 growth and the separation of the outer layers might then become 

 feasible. According to Dr. D. Spence the bark could be very easily 

 separated from the wood on a large scale even in irregularly shaped 

 plants by soaking in hot, dilute, caustic soda solution. The young 

 shoots are long, straight, and erect in viridulus; similar l)ut shorter 

 in graveolens and consiniilis; yery much branched and twiggy in 

 (jnaphalodes and hololeticns. In all of these forms they are covered 

 with a closely packed gray, green, or white felt-like tomentuin which 

 is deciduous only after several years. The narrow entire leaves are 

 rather sparse and may be either green, as in consi))iih\'i and gravrolens, 



