PLANT LICE. 175 
the interior regions of the same latitude in spite of the much 
colder winters. The root form survives the winter usually in 
an immature condition, viz, larva in various stages of develop- 
ment, and both in latitudes where the aerial forms are killed 
by the severity of the winter and elsewhere it seems probable that 
there is a regular upward migration in spring and early summer 
from the roots, the aerial colonies appearing first near the crown 
and at a later period on the higher parts of the tree. At any 
time during summer and fall there may be migrations to the 
roots, and throughout the year the subterranean colonies are 
maintained. 
“The spread of the insect is accomplished in part by the 
viviparous females, which appear in late summer, but quite as 
commonly perhaps by the transporting of young or partly grown 
individuals from tree to tree or to distant orchards by means 
of birds or insects to which they have attached themselves. Its 
wide distribution is usually dependent on the traffic in nursery 
stock.” . 
“The most generally recommended measure hitherto is the 
use of hot water, and this, while being both simple and inex- 
pensive, is thoroughly effective, as has been demonstrated by 
practical experience. Water at nearly the boiling point may be 
applied about the base of young trees without the slightest danger 
of injury to the trees, and should be used in sufficient quantity 
to thoroughly wet the soil to a depth of several inches, as the 
lice may penetrate nearly a foot below the surface. To facilitate 
the wetting of the roots and the extermination of the lice, as 
much of the surface soil as possible should be first removed. 
“Some recent very successful experiments conducted by Mr. 
J. M. Stedman have demonstrated the very satisfactory protective 
as well as remedial value of finely ground tobacco dust. The 
desirability of excluding the aphis altogether from nursery stock 
is at once apparent, and this Mr. Stedman has shown to be 
possible by placing tobacco dust freely in the trenches in which 
the seedlings or grafts are planted and in the orchard excavations 
for young trees. Nursery stock may be continuously protected 
by laying each spring a line of the dust in a small furrow on 
either side of the row, and as close as possible to the tree, cov- 
ering loosely with earth. For large trees, both for protection 
