THE GEAPE PHYLLOXERA IN CALIFORNIA. 29 
upper side of the leaf; (2) several parthenogenetic generations to 
which the stem mother gives rise, some of which settle on the foliage 
and produce new galls, as gallicoles, while others repair to the roots 
and settle on them as radicicoles; (3) parthenogenetic generations 
on the roots descended from the phylloxerse which went from the 
foliage to the roots; (4) winged migratory forms, comprising a very 
variable percentage of the root and gall forms, produced in summer 
and autumn, which fly or are transported by wind to other vines and 
oviposit either under the bark or on the leaves; (5) the true sexes, 
which are wingless and beakless; (6) the winter egg, deposited under 
the bark by the sexed female after coition; (7) radicicoles, born on 
roots in the late autumn, which pass the winter thereon as small 
hibernants, mature the spring following, and give rise to radicicole 
generations which succeed one another during the summer and 
autumn. This, briefly, is the life cycle that occurs in parts of 
Europe where American vines are used for stock, and in the eastern 
and southern United States on the wild grapes and on varieties de- 
rived from them. 
It will be observed that the winter may be passed in two forms — 
the winter egg and the hibernant, the former on the aerial and the 
latter on the subterranean or root portion of the vine. On certain 
wild grapes, as Vitis riparia, V. rupestris, and V. berlandieri, and on 
hybrids from these species, the former is the normal form, and hiber- 
nating larvae are rare. On species like Vitis labrusca, V. monticola, 
and their derivatives, both forms may occur. On viniferse {Vitis 
vinifera) the latter form is by far the more common. In the 
majority of European grape districts both forms occur, the former 
on American resistant vines and the latter on viniferse, but in other 
localities, even where resistant vines are used, the winter egg is very 
scarce. These include certain regions of France and California, and 
it appears that in California the hibernant is normally the only form 
that passes the winter. 
The suppression of the winter egg, and, therefore, of the succeeding 
gall form, brings about a modified life cycle in the California vine- 
yard which may be briefly described as follows : ( 1 ) The hibernant 
radicicole passes the winter as a larva on the roots and occasionally 
on the trunk beneath the bark. (2) The hibernant, when mature, 
gives rise to generations of radicicoles, and the aphids that issue 
from eggs in late autumn become hibernants. (3) A certain per- 
centage of radicicoles, varying from causes such as humidity, tem- 
perature, condition of food, and variety of vine, develop into winged 
migrants and issue from the ground. (4) Radicicole larvae forsake 
the roots and seek to reach other vines either by way of the soil 
surface or through subterranean passages such as cracks. 
