100 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 
shade temperature of 90° F., eggs exposed to sunlight were killed 
in 20 minutes. At a shade temperature of 76° F., 40 minutes' exposure 
to direct sunlight killed all aphicls, but when placed in the shade 
the eggs resisted the maximum test of 60 minutes' exposure. 
It is therefore apparent that eggs can resist the sun's rays to a 
considerable extent. The extent of their resistance to atmospheric 
temperatures in the shade can not be estimated, though it is of course 
greater than their resistance to direct sunlight. The eggs utilized in 
these tests were selected at random, and therefore were in various 
stages of embryonic development. 
Experiments with the submersion in water of active newly hatched 
larvae are detailed under the heading " Diffusion," which follows. 
DIFFUSION OF PHYLLOXERA. 
In European countries four natural means of diffusion are recog- 
nized: (1) By the winged insect; (2) by newly hatched wandering 
larvae issuing from the soil; (3) by newly hatched wandering larvae 
traveling through the soil; (4) by the gall-inhabiting form. To 
these there should be added casual means, as follows: Cultivating 
instruments, vine supports and picking boxes, plants between the 
vines, man and domestic animals, water, cuttings and rooted vines, 
phylloxerated land, and old stumps. 
DIFFUSION BY FLIGHT. 
Comparing the slower diffusion of the phylloxera in California 
with that of certain European vine-growing sections, it was from the 
first doubted that the winged form was a common diffusing agency, 
in spite of the fact that its production is often abundant in California 
vineyards on the roots of vines the second and third years after the 
initial infestation. This doubt became strengthened by (1) lack of 
leaf galls in nature and failure to discover winter eggs on a large 
number of vines of different varieties known to have been infested 
by migrants, or to have been close to vines thus infested; (2) the fact 
that, in confinement, during five years, thousands of migrants were 
utilized and only 72 sexual forms were secured, and, in turn, no 
normal winter eggs. On comparing the researches of European 
observers it is found, however, that in most cases they were unable 
to raise the sexual forms in confinement in any numbers, so this 
second point is inconclusive. 
Grassi (11, p. 138-148) and his colleagues demonstrated that the 
insect which hatches from the winter egg always settles on the young 
vine leaf and becomes the gall-making stem mother (gallicole). 
They also found (11, p. 274-280) that there occurred a nymphlike 
form which deposited parthenogenetic eggs from which issued root- 
