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euphorbiacese, and the apocynese, descend also 

 at certain seasons. Notwithstanding a great 

 equality of temperature, the trees of the torrid 

 zone follow a cycle of vegetation, of changes 

 periodically returning. The existence of the 

 dapicho is more interesting to physiology, than 

 to vegetable chemistry. Mr. Allen has pub- 

 lished a memoir on the difference observable 

 between the caoutchouc in it's ordinary state, 

 and the substance from Javita, which I sent to 

 4 Sir Joseph Banks. A yellowish white caout- 

 chouc is now to be found in the shops, which 

 may be easily distinguished from the dapicho, 

 because it is neither dry like cork, nor friable, 

 but extremely elastic, glossy, and soapy. I 

 lately saw considerable quantities of it in Lon- 

 don, the price of which varied from six to fif- 

 teen franks a pound. This caoutchouc, white, 

 and greasy to the touch, is prepared in the 

 East Indies. It exhales that animal and fetid 

 smell, which I have attributed in another place 

 to a mixture of caseum and albumen. * When 



* The pellicles, which the milk of hevea in contact with 

 the atmospheric oxygen deposits, become brown on expo- 

 sure to the sun. II' the dapicho grow black as it is softened 

 before the fire, it is from a slight combustion, from a change 

 in the proportion of its elements. I am surprised, that some 

 chemists consider the black caoutchouc of the shops as mixed 

 with soot, as blackened by the smoke to which it has been 

 exposed. {Thomson's Chemistry, 1818, vol. iv, p. 197.) 



