186 



Guayule. 



Table 53. Analysis of irrigated plant two years old from transplanted stocks, Cedros. 

 Collected April 4, 1909. Plant weighing 4.5 pounds fresh. 



(I) The original stump planted March 1907, divested of its subsequent growths. 

 (II) The growth of 1907 separated into wood and cortex: the wood (Ila), the 

 cortex (bark) (lib). (Ill) The growths of 1908 intact, and therefore comprising 

 both wood and cortex. (IV) The growth of 1909, consisting of short new twigs 

 and their leaves, developed before the date of collection. (V) The lateral roots 

 intact. 



The method by which the above data were obtained was worked out 

 by my former colleague, Dr. Whittelsey. The method was controlled by 

 myself microscopically, and the material was found after treatment to 

 have been thoroughly, though not quite entirely, extracted. The error 

 from this source, as shown by this control, is, however, extremely small, 

 and the figures may be accepted as practically correct. 



For the purpose of appreciating the practical significance of the data, 

 we may compare the percentage of rubber in the new growth intact. For 

 field plants we have a 9.7 per cent rubber-content. In the twigs of the 

 irrigated plants studied the amount is 3.3 per cent, namely, a little over 

 one-third that of field plants. By comparing Ila and 116, we note that 

 this low percentage is due, as shown in Chapter V, to the low percentage 

 of rubber in the wood and its relatively larger volume in irrigated plants. 

 Moreover, the "branches and twigs" of Whittelsey 's table can not be 

 directly compared with those of III in my own, but rather with II and 

 III taken together. If it were possible to compare the cortices alone 

 we should find, in all probability, a percentage of about 4 per cent of rub- 

 ber for irrigated plants against 15 to 20 per cent for field plants, so that 

 for the new growths under irrigation from the transplanted stocks in 

 question the amount of rubber formed by cortical tissues is about one- 

 fourth to one-fifth of that formed in the corresponding tissues in the 

 smaller branches and twigs of field plants. But the rate of growth under 

 irrigation is such as to result in the production of a volume of cortical 

 tissues, at the very least five times greater for the same length of time. 

 This factor would be very much increased if field and irrigated seedlings 

 were compared. The conclusion would therefore appear to be reached 

 that the difficulty attached to the problem of cultivating guayule for the 

 rubber is not that of obtaining rubber, but of properly handling the raw 

 material so as to extract the rubber from the tissues. 



In the first place, we have repeatedly noted the relatively large vol- 

 ume of the wood cylinder in irrigated plants, and its density. We have 

 also seen that the branches are long and lithe. If this material is handled 

 in its entirety, the volume of barren material which must be handled by 

 machinery is considerably greater than in the case of field plants. The 

 suggestion (Whittelsey, 1909, p. 6) that the cost of manufacture could 

 be reduced by the use of decorticating machinery, as is done in the case 

 of "grass rubber" (Funtumia spp.) in Africa, is still more pertinent for 



