586 
Journal of Agricultural Research 
Vol. XIV, No. 13 
especially numerous on the highest points of the cloth covering these 
pots, about a foot above the surface of the soil, and could be easily dis¬ 
lodged by slight puffs of air. Some were found under conditions which 
indicated that they were about 3 feet away from the nearest point where 
they could have originated. 
As the season advances, the wingless viviparous females give birth 
to individuals which develop into winged viviparous females (sexupara), 
which later leave the soil and fly away. 
DATES WHEN WINGED MIGRANTS (SEXUPARA) ARE FOUND IN THE 
SOIL 
A few winged females have been found in the soil as early as December 
12, and, as is the case with the winged females occurring in the galls, 
their number gradually increases as the season advances. During 1917, 
roots of Coronopus didymus were examined in the field from time to time 
with the idea of ascertaining how late in the spring the species occurs in 
the soil. The last winged individuals were taken on April 9. On April 
16 no subterranean forms could be found, though winged migrants were 
alive on poplar as late as April 30. 
From the field observations it appears that these winged migrants fly 
from the crucifers to the poplar trees during the spring, where, usually 
in some suitable crevice, they give birth to the true sexes. Winged 
females, agreeing with the winged females found about cruciferous roots, 
were found in such locations on poplar trees during March and April, 1917. 
Some observed on March 20 were dead, with true sexes and eggs located 
near by. 
NUMBER OF YOUNG TO WHICH WINGED MIGRANTS (SEXUPARA) 
FROM CRUCIFERS GIVE BIRTH 
In the laboratory, under conditions quite different from those under 
which the winged migrants would live in the field, the greatest number of 
sexed individuals to which a single aphid was observed to give birth was 
six. Usually this winged form brings forth all of her offspring within a 
short time and then dies. Those kept in the laboratory were examined 
daily, all of the young usually being produced from the time of one exami¬ 
nation to the next. Individuals of both sexes have come from one winged 
migrant. 
Examination of the abdomens of several winged migrants, collected 
from soil about the roots of crucifers, showed them to contain from 
four to seven sexed specimens, seven being the predominating number. 
DEVELOPMENT OF THE TRUE SEXES (SEXUALES) 
Eggs have been obtained in the laboratory from true sexes kept without 
food. The number of molts which the males and females undergo has 
not been ascertained, nor has it been learned when copulation takes 
