Sexual and Parthenogenetic Forms a34 
Wingless parthenogenetic individuals are found during the 
winter on the roots, where they cause swellings, or gall-like 
thickenings. Immense damage has been done to the vineyards 
of Europe by these root-inhibiting forms. At the end of June, 
winged parthenogenetic individuals develop, and wander up- 
ward to the leaves. They deposit eggs of two kinds, — large 
ones that produce the sexual females, and smaller ones that 
produce the males. The males and females pair, and the fe- 
male deposits on the bark a single large winter egg. In the 
spring this egg produces a wingless female that goes to the 
leaves and produces there gall-like growths. Offspring are 
produced, some or all of which find their way in time to the 
roots, where they remain over winter. 
In the phylloxerans of the hickories the life history is somewhat , 
thesame. Following Pergande the cycle for most of the Ameri- 
can species is as follows: From the winter egg a female — the 
stem-mother —is produced. She wanders to the young leaves 
and fixes her proboscis in the under surface. A gall develops 
around her, within which she lays eggs that give rise to winged 
migrants. ‘These leave the gall by the opening on its under 
surface, and fly away. Those that alight on the bark of the 
hickory deposit their eggs in its crevices. These eggs are large 
or small, and produce respectively female or male individuals. 
These pair, and the female lays a single large egg that over- 
winters and gives rise in the following spring to the stem-mother. 
In a few species the stem-mother produces forms that are, as 
a rule, without wings. These deposit the large and small eggs 
within the gall. Presumably the sexual forms that hatch from 
these eggs leave the galls and deposit the fertilized egg on the 
stem. 
The life histories of these different forms offer many points 
for consideration, and what is more important would seem to 
give unusual opportunities to test the factors that lead to the 
transformations of one form into another. What would happen, 
for example, if the life-cycle were to be artificially altered at dif- 
ferent points in its course by transferring the individuals prema- 
