RUBBER OF YOUNG TREES INFERIOR. 65 



Resin in rubber from — Per cent. 



Trunk 2. 61 



Largest branches 3. 77 



Medium branches : - 4. 88 



Young branches 5. 86 



Leaves 7. 50 



If these figures represent facts at all general, they lessen very dis- 

 tinctly the prospects of any plans which contemplate the tapping of 

 very } 7 oung trees, and it will be necessary to agree with Dr. Weber 

 that eight years is the minimum age at which a plantation can be 

 expected to furnish rubber for the market. 



But as this point is one which has been brought into considerable 

 prominence in recent years, and is being relied upon by some as a 

 means b}^ which the profits of rubber culture can be increased and 

 hastened, it may be well to state that the inferiority of the rubber of 

 young trees and growing parts has been determined by other compe- 

 tent investigators and especially by Mr. Parkin, whose account of the 

 matter furnishes several interesting details which supplement the 

 figures furnished by Dr. Weber: 



In the case of Hevea, the rubber collected from the young stems and leaves, as 

 well as from the unripe capsules, is somewhat adhesive, and has less elasticity and 

 strength than that from the trunk-. In the Castilla introduced into Ceylon the latex 

 from the stems bearing leaves, as well as from the leaves themselves, molds between 

 the finger and thumb into a very sticky substance, wholly unlike the caoutchouc- 

 containing latex of the trunk. It dries to a brittle material, which becomes viscous 

 when warmed. The quality of the rubber from stems of this Castilla, 12.5 to 25 

 centimeters (5 to 10 inches) in circumference, was likewise tested. It seemed to 

 have properties intermediate between that of the shoots and the trunk, being slightly 

 sticky and somewhat deficient in elasticity. 



The climbing rubber plants, Landolphia kirkii and Urceola esculenta, show a sim- 

 ilar difference between the latex from the shoot and that from thick stems. Ficus 

 elaslica also exhibits this peculiarity. a 



Attention was called to this in Ficus as far back as 1839 by Wein- 

 lung. He called the substance "viscin," and considered it interme- 

 diate between resin and caoutchouc. 



Mr. Parkin further says: 



In many plants this so-called viscin seems to occur throughout the laticiferous 

 system, e. g., the common bread-fruit (Artocarpus incisa) and jak (A. integrifolia) , 

 trees of the Tropics. 



Most likely there are bodies which do not come within the categories of caout- 

 choucs and guttas, and yet are hydrocarbons with the same percentage composition. 

 Probably some of these viscous substances are such. Also it appears probable that 

 all caoutchoucs are not identical, and that when prepared as pure as possible from 

 the latex, as by the ingenious centrifugal method of Biffen, it may be found, for 

 example, that the caoutchouc of Hevea has slightly different properties from that of 

 Castilla. & 



« See Weiss, Trans. Linn. Soc, 111, 1892, p. 243. 

 & Parkin, Annals of Botany, 14: 203-204, 1900. 



4876— No. 4:9—03 5 



