Pi Peat pe 
On Mildew. By Timothy Pickering. 
Read March 13th, 1810. 
| Washington, January Ist, 1810, 
Dear Sir, 
In a conversation with you on mildews, I mentioned 
a short but very ingenious dissertation on that subject, 
which I had often quoted on the like occasion, and 
which I promised to send you. It was published in a 
Boston newspaper in the year 1768; 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 my faith in the 
correctness of the “‘ New-England-man’s” theory. Sir 
Joseph’s (to the naked eye) invisible seeds of fungi, 
find, in the extravasated juices of the leaves and stalks 
of grain, a ded 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 and 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 
