1 i'l ^M UaU-Goodspofd : ( 1> rysil 249 



laid down. Finally, with the appearance of the phellogen deep in the 

 cortex and the production by it of a few layers of cork the rubber in 

 the cells external thereto begins to degenerate and soon loses its char- 

 acteristic staining capacity. It is true, of course, that the annual in- 

 crements added intracambially to the primary medullary rays and 

 which in part are devoted to the origination of secondary rays in- 

 creases each year the number of cells in the woody cylinder available 

 for rubber deposition. There is in this case, obviously, no such annual 

 reduction in the amount of rubber bearing tissues as is characteristic 

 of the cortex. The amount of new rubber bearing tissue added each 

 year to the existing ray material is so small and the quantity of rub- 

 ber present in the individual ray cells is so relatively diminutive, that 

 this source of increase in the rubber content of old as compared with 

 younger stems is negligible. 



The problem of a seasonal or periodic deposition will re(|uire for 

 its final solution a much more detailed study than we liave been able 

 to give to it. The experiments mentioned on page 246 seem to indicate 

 that the maximum amount of rubber is present near the close of the 

 growing season. If these results are confirmed they will have a 

 directive influence in determining the season at which harvesting 

 should take place. This probably would not be a determining factor 

 in selecting the season for harvesting wild shrub, but it might mean 

 the difference between financial success and failure when the handling 

 of cultivated plants is under consideration. 



It would follow from the foregoing that old plants would be the 

 best rubber producers. It is evident that as the plant becomes over- 

 mature decay sets in and reduces the weight of the rubber earrjang 

 portions. This is borne out to some extent by the results of our 

 analyses, which indicate that the average percentage composition is 

 about the same for large old plants as for medium sized plants of 

 moderate age. Young plants, say four years old or less, are almo.st 

 always low in percentage content, a direct result of the fact that 

 deposition is small until about the third year and the ratio of rubber 

 bearing tissue to the whole plant is therefore low. This discrepancy 

 gradually disappears with age. It is quite certain that shrub which 

 has reached maturity, that is, six to ten years for the viridiihis form. 

 bears its maximum quantity of rubber. 



The depth at which the plants may be cut in harvesting without de- 

 stroying the power of regeneration is a matter which has received con- 

 siderable attention because of its practical bearings. Histological and 



