On Mildew. 167 



My fixed opinion then is, and long has been (in 

 which I since find I agree with the famous M. Chateau- 

 Vieux) that the powder which fornns the rust, called 

 mildews, is the extravasated juice of the plants dried by 

 the sun, upon the stalk. 



My reasons are these, 1st. The grain, we see, re- 

 ceives no more nourishment after it is violently struck. 

 2d. On a careful inspection, it appears that some of 

 these rusty blisters are actually under the outer coat or 

 skin of the stalk, and do not appear to have any com- 

 munication from without, others are only split in the 

 middle, some more and some less, and the rust appears 

 on the outside more or less according to the opening. 

 3d. The learned Mr. Tillet (Duhamel tells us) with a 

 good microscope, actually saw the juice issuing from 

 these small openings, over which he still perceived some 

 pieces of the membrane which imperfectly covered 

 them. This methinks must give occular demonstration. 

 But the two former satisfied me, the second especially 

 appeared demonstrative. 



The true cause of this extravasation is next to be in- 

 quired into. This no writer that I know of has hinted. 

 I take it to be this, a sudden obstruction of the juices of 

 the plant, by a very cool night, after several days and 

 nightsof very warm weather. 



By a continued heat, the earth is warmed to a great 

 degree, and all nature invigorated ; this occasions a 

 great ascent of the juices, so that every vessel is full 

 (as in an animal of a plethorick habit when all know 

 there is most danger of the vessels bursting ;) a sudden 

 cold ensuing at this critical season chills the tender 



