256 
tainly insects may be found feeding’ upon the mealy 
substance produced. There is commonly found in 
the middle of summer, a very minute reddish 
coloured larvae feeding, which for some time kept 
me wavering as to whether it was the cause, but I 
am now decided that it is not, which may easily be 
proved by noticing plants of any kind subject to 
the Mildew early at the spring, at its first appeai’- 
ance, with the aid of a glass, at which period these 
little animals are not in existence. Aphides may 
be found upon some of these shoots, but they pro- 
duce no such effect. 
The cause presenting itself to me as most 
likely, is from the sap being disordered somehow 
or other, either in setting of from the roots, by 
absorbing improper nutriment, or in its ascent 
through the arteries of the branches, or probably 
in the process of elaboration of the sap which is 
said to take place chiefly in the leaf, from the finer 
vessels of which a poi’tion of the sap transpires. 
It is probable that the sap in passing through this 
process, or in circulating thi-ough the various vessels, 
either in the ascent or descent, either by internal 
or external obtrusion becomes disordered, so as 
not to be evaporated or dissipated in fine vapour, 
but to be discharged from the leaves and young 
W'ood in a thick grossy state ; and to accumulate 
on the infected part, and exhibit the disease in the 
state we find it. 
It is doubtful whether any external applica- 
tion, as ))rescribed by some of the foregoing au- 
