134 



The same writer also gives a table showing the varying amount 

 of resin in samples from different parts of the same tree : 



Resin in Rubber from — Per cent. 



Trunk ... 2. 6 1 



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 

 distinctly the prospects of any plans which contemplate the tap- 

 ping of very young trees, and it will be necessary to agree with 

 Dr. Weber that eight years is the minimum age at which a plan- 

 tation can be expected to furnish rubber for the market. 



But as this point is one which has been brought into considera- 

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

 as a means by which the profits of rubber culture can be increased 

 and hastened, it may be well to state that the inferiority of the rub- 

 ber of young trees and growing parts has been determined by 

 other competent 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 c >llected from the young stems and leaves, as 

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

 strength than that fr^m the trunk. In the Oastillo.i introduced into Ceylon the 

 latex from the stems bearing leaves, as well as from the leaves themselves, moulds 

 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 f r )m stems of this 

 Castilloa, 12.5 to 25 centimeters (5 to 10 inches) in circumference, was likewise 

 tested. Ir, 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 

 similar difference between the latex trom the shoot and that from thick stems. 

 Ficus clastica also exhibits this peculiarity.a 



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

 Weinlung. He called the substance "viscin," and considered it 

 intermediate between resin and caoutchouc. 



Mr. Parkin further says : 



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

 system, e.g., the common breadfruit (Artocarpus incisa) and jak (A. integrifolia), 

 trees . f the Tropics. 



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

 choucs and guttas, and yet are hydrocarbons with the same percentage composi- 

 tion. Probably some of these viscous substances are snch Also it appears pro- 

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

 po.ssible from the latex, as by the inyenicms centrifugal method oi Biffen, it may 

 be found, for example, that the caoutchouc of Hevea has slightly difi'erent proper- 

 ties from that of (JastilJoa.fo 



: ' (To be continued.) 



a See Weiss, Trans. Linn. Soc. Ill, 1892, p. 243. 

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



