308 
work showed that a 15 per cent, emulsion was injurious to the tree, 
taking nearly all the leaves from the box-elders and the lindens, and 
half those from the soft maples. In this same year ( 1904) Mr. S. A. 
Johnson, of the Col. Agricultural Experiment Station, made a num- 
ber of laboratory experiments with the summer treatment of this 
insect, reaching the conclusion that after the young are a week or 
ten days old they are not easily killed by the kerosene emulsion, but 
that before reaching this age they may be effectively treated by 
sprays of as low a strength as 5 per cent. 
The following year (1905) Dr. J. W. Folsom, of the University 
of Illinois, made for me a series of experiments, opportunity for 
which was provided by the courtesy of Mr. O. C. Simonds, Super- 
intendent of Graceland Cemetery. 
A 10 per cent, emulsion of kerosene was applied to several trees 
of medium size with the use of a Bordeaux nozzle on an extension- 
pole. A solid stream was first directed against the egg-masses in order 
to loosen and soak them, after which a very fine spray was applied 
as thoroughly as possible to both sides of the leaves. A solution of 
whale-oil soap (one pound to six gallons of water) was applied to 
an eighth tree by the same apparatus and with the same care. 
The effect of the spray was tested by counting both dead and 
living scales on twenty-five leaves picked at random from different 
parts of each tree, one series of counts being made just before the 
spray was applied and another as soon as possible after it had dried 
away and taken effect. Among the trees receiving the 10 per cent, 
emulsion of kerosene were one tree sprayed July 3, at the beginning 
of the hatching period of the scale, one treated July 11, at about 
the middle of this period, three treated July 19 and 20, at the end 
of the period, and one treated twice, once at the middle and once at 
the end. The tree receiving the soap solution was sprayed July 19 — 
that is, at the end of the hatching season. 
Four hundred and eighty-four thousand scales, borne by four 
hundred and fifty leaves from these various trees, were critically 
examined, and classified as either living or dead. The ratio of bene- 
fit — the percentage, that is, of scales actually killed by the spray — 
was determined in all cases by eliminating from the calculation the 
scales dead at the beginning of the experiment, and figuring the per- 
centages only on the number of scales alive when the spray was ap- 
plied. The following table gives the essential data and results of 
these experiments. 
