182 MANUAL OF GARDENING 
cation of poison to the parts 
that they eat. It is apparent, 
however, that insects which 
suck the juice of the plant 
are not poisoned by any 
liquid that may be applied 
to the surface. They may 
be killed by various mate- 
rials that act upon them ex- 
ternally, as the soap washes, miscible oils, kerosene 
emulsions, lime-and-sulfur sprays, and the like. 
There has been much activity in recent years in the 
identification and study of insects, fungi, and micro- 
organisms that injure plants; and great numbers of 
bulletins and monographs have been published; and 
yet the gardener who has tried assiduously to follow 
these investigations is likely to go to his garden any 
morning and find troubles that he cannot identify and 
which perhaps even an investigator himself might 
not understand. It is important, therefore, that the 
gardener inform himself not only on particular kinds 
of insects and diseases, but that he develop a re- 
sourcefulness of his own. He should be able to do 
something, even if he does not know a complete 
remedy or specific. Some of the procedure, prevent- 
ive and remedial, that needs always to be considered, 
is as follows: — 
Keep the place clean, and free from infection. 
Next to keeping the plants vigorous and strong, 
this is the first and best means of averting 
trouble from insects and fungi. Rubbish and 
all places in which the insects can hibernate 
and the fungi can propagate should be done 
away with. All fallen leaves from plants that 
217. Canker-worm. 
