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Infectious difeafes in the animal creation may 

 be communicated in two ways. One clafs of dif- 

 orders can be communicated only by defcent from 

 parent to child, and can never be communicated by 

 juxta pofition : another clafs of difeafes can be com- 

 municated merely by juxta pofition, and not at all 

 by defcent of blood. Does fuch a diftinction as this 

 prevail among vegetables? Has any experiment 

 been recorded, which proves that any particular dif- 

 eafe among plants can be conveyed by juxta pofi- 

 tion only? Is not the fmut in wheat of this clafs ? 

 May it not extend to others ? May not a few in- 

 fected potatoes in this way, if mixed in a large heap, 

 like a fubtile leavening principle, infect the whole ? 

 Experiments are here much wanted. 



But I am far from alledging, that, though it were 

 an eftablifhed fact that potatoes had been known 

 to be much more infected with the curl, than thofe 

 from whence the feed was obtained had been in the 

 former year, it would either prove that the difeafe 

 might originate from other caufes than contami- 

 nated feed, or make it certain that befides direct 

 defcent, the diforder could be communicated merely 

 by juxta pofition. For though it mould fo happen, 

 that the diforder could be communicated only by 

 direct defcent, the fact above-mentioned might 



poflibly 



