STATE AGRICULTURAL SOCIETY. 
449 
HOP-APniS. INFLUENCE OF THE WEATHER IN PRODUCING IT. 
tions. It is proper, therefore, that I here adduce some of the evidence 
which I have, upon this particular point. 
It is over twenty years ago that I first noticed this blackness as being occa¬ 
sioned by plant-lice. Among several willow trees by the side of a stream 
near my residence, there was one so thronged with the Willow-aphis that I 
\tant several times to that tree to contemplate the spectacle which these 
insects presented. And all through the following winter, no person passing 
within sight of that tree could fail of noticing the blackness of its trunk and 
limbs, it being the more remarkable as none of the other willow trees around 
it had any tinge of this color. The thought thereupon became impressed 
upon my mind, that it was the plant-lice with which this tree had been so 
overrun the preceding summer, which had in some way imparted this black¬ 
ness to its bark. Two or three winters afterwards, I noticed the same black¬ 
ened appearance to a pine tree, which tree I knew had been thronged with 
Aphides the summer before. I need not specify the several other instances 
of this phenomenon which I have noticed. Several years since, when T was 
investigating the aphis of the apple tree, I discovered that, in addition to the 
bark of the trees, the leaves also acquired this sooty appearance from these 
insects; and then upon giving this subject a particular examination, I became 
assured that this black substance was merely the honey dew in a decomposed 
state. 
Some writers have remarked that dry weather causes the several kinds of 
plant-lice to increase and become pests to the different species pf vegetation 
which they respectively inhabit; and my own observations incline me to regard 
this remark as being correct. During the dry period in June which frequently 
succeeds the spring rains, I have in particular years noticed these insects as 
occurring in unusual numbers, whereupon I have apprehended that, having 
acquired such a start so early in the season, they would prove to be the most 
pernicious insects of the year; but rainy weather coming on after this, they 
have seemed thereupon to decline and have ceased to attract further attention. 
Hence I think it true as a general rule, that dry weather favors and wet 
weather retards their increase. And at first thought, this view is further 
strengthened by the fact that this aphis upon the hops was so excessively 
numerous the past summer, when we experienced a drouth of such protracted 
length and severity. But, on the other hand, these insects were similarly 
numerous the year before, when the summer was unusually wet. We are thus 
assured there is some influence more potent than the hygrometric state of the 
atmosphere, which has brought them forth in such hosts upon the hops. F. 
W. Dogget, Esq., read a paper “Upon the weather in connection with Aphis 
Blight and the growth of Hops,” before the London Meteorological Society, 
Nov. 28, 1854, a report of which we meet with in the Gardener’s Chronicle of 
that year, p. 820. Mr. Dogget found, on comparing the fall of rain each 
month for a period of thirty-eight years, that “ the years in which an excess of 
rain had fallen in or about the three mouths ending in September of the pre¬ 
vious year —the three following months and the March following being both 
comparatively deficient in rain — were followed by a short crop of hops, arising 
from the Aphis blight; and on the contrary, when the quarter ending Septem- 
[Ag. Trans.] - 29 
