Puant Lice Insuring FoutaGE AND FRUIT OF THE APPLE 717 
in color, and is covered with a glutinous substance which hardens with 
age. The color gradually changes to greenish yellow and finally to a 
shining jet-black. The time required for this change in color varies under 
normal outdoor conditions from about nine days to more than two weeks. 
The production of winged forms 
In the case of Aphis pomi the production of winged forms is for one 
purpose only; this is distribution, not migration to different host plants. 
For this purpose it is essential that the early generations should provide 
a very high proportion of winged forms, so that advantage can be 
taken of the large numbers and widespread occurrence of the host 
plant (apple). This is exactly what takes place in nature, over 75 per 
cent of the second generation and between 25 and 50 per cent of the third 
generation acquiring wings. Such a large proportion of winged forms 
so early in the season insures a widespread distribution and does not call 
for any marked production of winged forms thruout the summer; and 
such a condition appears to be the normal one for this species. Smith 
(1900 a) states that no winged forms are produced after the third genera- 
tion. Sanderson (1902) and Gillette (1908) report winged forms occa- 
sionally appearing as late as the last of August. In the rearing-cage 
work practically every generation produced a few winged forms. In the 
fourth generation very few winged forms appeared, but fully 50 per cent 
of the fifth gencration were winged. In all other generations except the 
ninth, the thirteenth, and the fourteenth, a few winged forms appeared. 
In the field winged forms were not uncommonly found during July and 
August, while in 1915 in the cages the last winged forms appeared on 
September 6. This would seem to indicate that practically all the genera- 
tions during any season do and can produce winged forms. Whether 
the direct descendants of the winged forms may also be winged has not 
been positively determ'ned for all generations. In all cases studied so 
far, the first generation from winged ancestry are always wingless, 
whereas the second generation may be either winged or wingless. Should 
this prove true for all winged individuals, the results would agree 
with those found by Professor Slingerland in his extensive studies of 
Aphis avenae.* 
- Manuscript notes by Professor Slingerland. 
