93 
single season during which this work has been under my charge, 
but the conclusions already reached have a definite and appreciable 
value, which will probably make them welcome as a contribution to 
the subject. 
HOT WATER. 
One of the applications most frequently advised is that of hot 
water at a temperature sufficient to destroy the worms, but too low 
to injure seriously the plants infested. A series of experiments upon 
the subject. made by Mr. Coquillet, of McHenry county, are de- 
scribed in the last report of my predecessor, Dr. Thomas, but as 
they were made at a time and place when the cabbage worm itself 
was not to be had, the conclusions arrived at are still open to ques- 
tion. As far as this species of caterpillars and plants experimented 
upon are concerned, Mr. Coquillet’s experiments seem quite conclu- 
sive, but as various species differ greatly in their power tc resist 
injurious conditions, the inference from the species used by him to 
the cabbage worm itself is not strictly warranted. For the purpose 
of testing the exact effect of water of different degrees of temper- 
ature upon the worm in the open air, and the cabbage plants 
attacked by them, I sent an assistant, early in September, into 
the field with an oil stove and a sprinkler, with instructions to 
test the matter thoroughly. The water was heated to a given tem- 
perature, as indicated by a good thermometer, and applied imme- 
diately to the infested plants. At 150° F., no effect whatever was 
produced upon either plants or insects. At 140° the worms were 
not injured, although they were apparently a little stupefied at first, 
and no perceptible effect was produced upon the plants. At —50° 
the worms were nearly all killed, but the cabbage plants themselves 
were also badly injured, the leaves, wherever the water struck, being 
parboiled, and subsequently withering. At 160° the same effect was, 
of course, produced, but was still more: marked. The cabbages at 
this time were well headed out, many of the worms were full-grown, 
and the others of various sizes from a half inch upwards. These 
experiments go to show that the worms are fully as hardy as the 
cabbages. 
POWDERED PYRETHRUM. 
The general efficiency of pyrethrum as an insecticide has been so 
fully attested, and its use for the protection of cabbages recom- 
mended upon so high authority, that the experiments were under- 
taken only for the purpose of exactly defining the conditions under 
which it could be most successly applied. The powder was obtained 
especially for this experiment from Messrs. Lehn & Fink, of New 
York, by whom it was said to have been recently imported from 
Kurope. The powder was mixed for the first experiment with ten 
parts of flour, and left to stand one night before being used. Four 
nearly full-grown worms were selected and brought to the labora- 
tory, where they could be carefully observed. The diluted pyrethrum 
was applied thoroughly with a powder-gun, and in ten minutes the 
worms all exhibited their uneasiness by quick, jerking motions. In 
fifteen minutes, they were crawling slowly about and writhing as if 
