^oO Univrrsihj of California Puhlicationa in Botdini | Vol. 7 



chemical analyses of Ihc loot indicate that it carries its highest per- 

 centage of i-iibher at about liic siii-face of the soil and that the per- 

 centage i-apidly tliininishes downward, iiiiti] at an avei-age depth of 

 al)out four inches the amount present is so small that the remainder of 

 the root is of no value. In harvesting, it would therefore be desirable 

 to make the cut about four inches below the surface. Our ('Xjx'riments, 

 performed on over three hundred plants of three leading varieties, 

 have definitely determined, however, that if this is done, or if the 

 root is cut oft' anywhere below its junction with the stem, the portion 

 remaining in the soil will die. The obvious explanation of this phe- 

 nomenon is thai, as in most plants, new shoots arise only from stem 

 tissue. In all cases where the stems were cut off just above the soil 

 surface the stumps promptly sent up an abundant growth of new 

 shoots. In one case a diagonal cut was made just at the surface so that 

 about an inch of stem was left on one side of the stump, while on the 

 opposite side the cut extended to about an inch below the top of the 

 root. After a lapse of six mouths there was a copious growth of shoots 

 two feet long from the higher side of the stump, none at all from the 

 lower. 



The line of demarcation between stem and root is not a sharp one. 

 A microscopic examination for dormant buds is, of conrse, impractical 

 in field woi-k ; the bark is so similar on the lower part of the stem and 

 tlic upper part of th(^ root that its texture and color furnish no clue; 

 and the soil level cannot be accepted as a criterion since it is easily 

 modified by disturbing agencies such as erosion, deposition, accumula- 

 tion of vegetable matter, and the activities of rodents. In most cases, 

 a cut made just at the first crotch, which is usually also at the original 

 soil surface, will safely provide for regeneration but much experience 

 will be necessary if one desires to obtain the maximum amount of rub- 

 bei- and at the sauK^ time be assured of new growth without replanting. 

 In case the wild shrub is ever utilized for an emergency supply of 

 rubber it will probably be best to make the cut at about six inches be- 

 low the surface, thus sacrificing the roots for the sake of the rubbei" 

 in tlicir upper portions; on the other hand, if Chrysotlunnniis is grown 

 as a field crop it will probably be found profitable to provide for vege- 

 tative reproduction, either by leaving an inch or so of stem oi- by leav- 

 ing portions of several of the lower branches as a foundation for a 

 lai'ger and bi-oader plant. 



The bulk of the shrub may be materially reduced without much 

 loss of rubbei- l)y cutting off and discarding all growtli less than thi'ee 



