Progress of Vdcchiation in India. 327 



fixed, one or more prolongations of the mcdullan- sheath 

 penetrating the wood, and sinking into the petiole, or inio 

 the base of the leaf to which they convey sap. In the spe^ 

 cies of the family of the pinn'if'cra one single prolongation of 

 the like kind enters into the petiole : in all the other vege- 

 tables which I have examined^ I found two, three, and e\ en 

 more. 



The fall of the leaves is explained, not only by the in- 

 fluence of the air and the sun, but also by the mechanism 

 of nature, which, according to the opinion most generally 

 admitted, prevents the sap from ascending frum the branch 

 to the petiole. '* The tubes of the Uhcr (it is said) in daily 

 extending more press against each other, and by a necessary 

 consequence transport themselves towards the centre of the 

 vegetable; at the same time the bark, w'lich dilates itself, 

 recedes; and the necessary result of these two movement? 

 is, that the leaves no longer receive sufficient nourishment." 

 There is no doubt that the influence of the air and the svm 

 contributes powerfully to harden the substance of the leaves, 

 .IS well as to approach towards the ligneous state, in which 

 the passage of the juices ceases, and then the leaves no 

 longer transpire or absorb. But I do not believe that the 

 mechanism in question can in any manner prevent the 

 ascent of the sap. But do we not, indeed, see that in a great 

 number of plants soine leaves drop at the period when the 

 liber has not yet been changed into allurnum, and while 

 the sap is still in full motion ? In a word, when the bark 

 is separated at the place where the petiole has been fixed, it 

 is seen that the prolongations of the medullary sheath, 

 which have conveyed the nourishing juice from the stem 

 to the leaves, are still green and herbaceous, and have sus- 

 tained no injury ; which seems to prove that they were not 

 choked, nor attracted with force. They dry a long time 

 after, and acquire very slowly the consistence of the wood 

 in which they are placed. 



N 



XLVIII. Progress of Vaccination hi India*. 



EVER was a discovery corroborated by more numerous 

 and distant evidences than the cow-pock. 



The bramins in India were accustomed to inoculate at 

 certain periods of the year ; now they vnccinate throughout 

 the year 3 and the following testimony has appeared in the 



* CommunicateJ by Dr. Ttsocnton, 



government 



