144 INJURIOUS INSECTS OF 1909 AND IQIO. 
The “cide’’ of these words means “kill.” An insecticide is some- 
thing that will kill an insect; a fungicide is something that will kill 
a fungous disease. Different kinds of compounds are used for 
the different kinds of insects and diseases. There is no one 
spray that is the “cure-all” for everything. For instance, insects 
that bite, like caterpillars and beetles, take one kind of insecticide; 
insects that suck, like plant lice and scales, require another kind of 
insecticide. One fungicide is good for one disease, but it may be 
worthless against another disease. The insecticides are usually 
separated into three groups: 
1. Gaseous insecticides. These are used in an enclosed space 
against either biting or sucking insects. Hydrocyanic acid-gas, 
carbon-bisulphid, and tobacco smoke come in this group. 
2. Contact insecticides. These are used against insects that 
suck their nourishment from plants through a proboscis-like beak, 
or against biting insects that cannot be induced to eat the parts of 
the plant covered with an internal insecticide. In this group are 
found the lime-sulphur washes, crude petroleum, kerosene, soaps, 
miscible oils, etc. 
3. Stomach or internal insecticides. These are used against 
insects that eat the foliage. The most important of these, like 
arsenate of lead, Paris green and arsenite of lime, contain arsenic 
in some form, and are called arsenical insecticides. The killing 
ingredient in these insecticides is not soluble in water, but is in the 
small particles of matter that remain in suspension in the liquid. 
The fungous diseases of plants are caused by minute parasitic 
plants known as fungi. Fungi, having no green coloring matter 
(chlorophyll), are reduced to the necessity of getting their food 
from other plants or animals, or from the dead remains of plants 
or animals. These fungi are composed of a great many threads, 
which gain entrance to the tissues of the host plant, and absorb their 
nourishment from it. Minute reproductive bodies, known as spores, 
are produced. One fungus may produce more than one kind of 
spore; during the growing season it may produce one kind, which 
is especially well fitted to reproduce the plant very rapidly, while 
later in the season it may form another kind of spore which will 
live during the winter and germinate the next spring. 
The cold-resisting spores may live during the winter in the soil, 
on the seed, on leaves, rotted fruit, or in rubbish. Further, the 
threads of the fungus may themselves live during the winter; they 
