C 1^4 1 



On Mildew, By Timothy Pickering. 

 Read March 13th, 1810. 



Washington^ January \st^ 1810. 



Dear Sir^ 



li: a conversation with vou on mildews, I mentioned 

 a short but ver) ingenious dissertation on that subject, 

 which I had often quoted on the hke occasion, and 

 which I promised to send 3^ou. It was pubUshed in a 

 Boston newspaper in the year 1 768 ; and the papers 

 for the year being bound in a volume, it was fortunately 

 preserved. A few days since I received the inclosed 

 copy, transcribed at my request. It gives the only sa- 

 tisfactory solution of the phenomenon of mildews that 

 I have ever met with. Sir Joseph Bankes's discoveries 

 (admitting their reality) did not abate mv faith in the 

 correctness of the " New- England-man's" theory. Sir 

 Joseph's (to the naked eye) invisible seeds of Jungi, 

 find, in the extravasated juices of the leaves and stalks 

 of grain, a bed adapted to their nature, in which they 

 vegetate. Those seeds, floating in the air, and striking 

 against the clammy juices of those plants, would of 

 course be there held fast aud take root. 



If you have visited the woods of Pennsylvania in the 

 spring, you must have noticed the rusty appearance of 

 the sap (particularly I think of the sugar-maple) oozing 

 from the stumps of trees felled not long before, and co- 

 vering the tops and sides of the stumps. Of the same 

 colour, you know, is the newly extravasated sap on the 



