284 — T. H. Morgan 
covered with galls—converted into a mass of galls in some cases— 
it is surprising that two stem-mothers do not oftener produce a 
common gall. When the galls are near together they crowd each 
other and flatten at the contact planes, but I have never found any 
communication between them. 
The size of the gall does not appear to depend on the presence of 
the second generation; for, in one case I found a large gall occupied 
by a single stem-mother without progeny. She must have been 
enfeebled or parasitized, yet the gall was fully developed. On 
the other hand if the stem-mother dies after the gall has begun and 
before she lays her first eggs, the gall ceases to grow. Experi- 
ments should be made to see if the gall will develop after the stem- 
mother is killed and only her early progeny left in the gall. he 
transfer of stem-mothers of different galls would also be profitable 
and might give interesting “hybrid galls.” 
The data indicate, if they do not prove, that the fertility of the 
stem-mother is intimately connected with the growth of the gall, 
and the growth of the gall in turn seems to depend on the condition 
of the leaf when it first begins to develop. The earliest galls 
develop rapidly and the stem-mothers in them lay the maximum 
number of eggs. Later galls remain small and the stem-mothers 
produce very few eggs. ‘That the result is due to the condition of 
the leaf when the gall is first formed and not to the time of year is 
shown by an observation [ made on this species in 1906. The 
buds on a certain branch were delayed as much as two weeks 
behind the others. When they did develop they became infested 
with P. fallax. The stem-mothers must therefore have waited 
two weeks for the bud to unfold yet the gall became full size. The 
converse point of view, that small galls are produced by weak 
mothers that will lay few eggs, may hold for some cases, but in 
general the facts indicate that it isthe condition of the plant rather 
than that of the animals that determines the fertility of the latter. 
Contrary to the behavior of other species of phylloxerans, the 
winged individuals of P. fallax may deposit their eggs within the 
gall. ‘his is indicated by the empty abdomen of some of the 
winged individuals. That others may emerge and deposit out- 
side seems also not improbable. This in fact would be the only 
