SECT. III. CIRCULATION OF JUICES. 241 



that they prove at the same time the circulation of 

 the vegetable fluids. For if it is admitted that the ^ 



descending proper juice forms not only a new epi- 

 dermis where wanted, and a new layer of liber and of 

 alburnum, but enters also, partly, the alburnum of 

 the preceeding year, where it mingles and is again 

 carried up with the ascending sap, it is obvious that 

 a sort of circulation is completed. But this last 

 and most essential part of the process rests merely 

 on the foundation of conjecture ; for there is no 

 proof offered in support of the fact : it is only said 

 that you cannot conceive how in a body so porous 

 as wood, the several fluids should remain unmixed. 

 It is, however, no proof of the truth of any opinion 

 to say that you cannot conceive the thing to be 

 otherwise, as the same thing has been said in sup- 

 port of ten thousand absurdities which have still 

 continued to be absurdities. It is no doubt difficult 

 to conceive how the fluids should remain unmixed ; 

 but what if they should remain unmixed after all ? 

 The alburnum of the former year being now con- 

 siderably condensed, will not afford that ready 

 reception to the proper juice which is here alledged : 

 in the same manner we shall suppose that the re- 

 turning vessels of the leaves do not admit coloured 

 infusions ; but if the vessels of the alburnum should 

 admit some part of the descending proper juice by 

 means of lateral communication as is here supposed, 

 can any one be certain that it is the juice which was 

 formerly carried up, and nat rather part of that 



VOL. II. R 



