THE GUAYULE 



3*9 



thin slice taken transversely through a smaller branch will enable us to 

 gain some impression of the structure and especially of the manner of 

 occurrence and distribution of the rubber. A twig about a vear old 

 taken at the end of a prolonged drought period will serve our purpose. 



Referring to Fig. 9, the reader will note that several concentric zones 

 of tissue ajmear. The outermost is cork (cA - ), which contains no meas- 

 urable amount of rubber in small branches. In old thick stems the 

 formation of cork in the deeper layers of the next occurring zone, the 

 cortex {cr in the figure), results in the cutting out of rubber-bearing 

 tissue, accompanied by a degeneration of the rubber itself, and its con- 

 secpient loss. The cortex comes next. It is made up of cells of uni- 

 form size and shape, containing chlorophyll, and hence green in color. 

 In each cell appears a large droplet of rubber, occupying nearly the 

 whole of the interior space (Fig. 9). Here and there are oval open- 

 ings which are sectional views of so many canals (re) which traverse 

 the cortex longitudinally. These contain a pale yellow resin, a com- 

 monly occurring material among the Composite. Any slight wound of 

 the cortex, however caused, may open one or more of these canals, and 

 the resin may then escape. Hardened, limpid drops of this, either 

 clinging to the branches or fallen on the ground beneath, are always to 

 be seen. The resin appears to be of little economic value, as it is soft. 

 During the mechanical extraction of rubber, it becomes mixed with up- 

 wards of 20 per cent, resin. 



Inwardly the cortex is broken up by radially placed masses of tissue 

 partly composed of hard "bast" fibers (&/. Fig. 9). These correspond 

 to the fibers of the flax in position and origin. Crude guayule rubber 



Pig. 8. An especially fixe stand of Guayule neab Las Caopas, 



Zacatecas, Mexico. 



