SOME ASPECTS OF SPRAYING AGAINST PESTS. 221 
Three different surfaces were used for the trial : an easily wetted 
one, the gooseberry leaf ; one wetted with moderate difficulty, the 
sea-kale leaf ; and one wetted with great difficulty, the summer stage 
of American gooseberry mildew. From the table one may see that 
gelatine and casein slightly increase the wetting power, while the 
stronger soap solutions still further increase it, but only by the 
2 per cent. 2 per cent, paraffin emulsion, by which is meant one 
containing 2 per cent, soap and 2 per cent, paraffin, is complete 
wetting of the mildew achieved. 
Having considered the necessity of wetting power in a contact 
insecticide, the lethal power remains to be discussed. Soap by itself 
and paraffin emulsions are to a certain extent lethal and may suffice 
by themselves in certain cases, but for the more resistant insects a 
more powerful poison is required. Of these the more commonly 
used up to now have been nicotine in some form and quassia. Were 
it not for its expense, nicotine would be an almost ideal insecticide, 
since it acts to a certain extent as a stomach poison as well. Quassia 
is an old-established substance, but suffers from the fact that to prepare 
it much boiling is needed. Certain of the coal-tar derivatives are 
frequently used in proprietary washes, but are often dangerous to 
foliage. Perhaps the only other contact insecticide in common 
use is lime-sulphur. Conflicting claims have been advanced for it, 
but the most recent experience seems to prove that its use is 
limited to the control of scale insects and that it has not much effect 
on others. There is in fact a decided dearth of suitable simple 
substances having an insecticidal value, and there is much room for 
chemical research in this direction. 
Spr ay -fluids Applied in the Semi-dormant State. 
There are certain advantages to be obtained by using a spray- 
fluid at this period instead of during the active season. The buds are 
just bursting, and there is thus a minimum of foliage, so that the tree 
can not only be far more effectively sprayed but much less spray fluid 
need be used. At the same time this very young foliage is surprisingly 
resistant to spray damage. Spraying during the active season usually 
means a certain interference with other operations of fruit culture, 
owing to withdrawal of the necessary labour, while in the spring labour 
can usually be more easily spared. The most important spray fluid 
employed at this time is the cover wash of lime, first introduced by 
Mr. Howard Chapman. Like many good inventions, it proved its 
value before its method of action was explained. It was originally 
used as a control measure for apple-sucker, and its use has been 
subsequently extended to the control of aphis. Considerable doubt 
existed at first as to the exact manner in which it acted. Many 
growers asserted that it was necessary to use the mixture as hot as 
possible, and urged that its good results were due to the causticity 
of the lime ; others suggested that the coat simply sealed in the eggs 
