356 
HARRY R. ROSEN 
while the growth of the tissue in which tke proboscis is working is 
arrested. Within thirty-six hours, the lower half of the leaf tissue, 
which is situated some distance from the portion attacked, begins to 
enlarge rapidly, giving rise to enormous hyperplastic growths. While 
the lower side of the attacked leaf has been growing enormously, the 
upper portion of the leaf directly beneath the insect, which shows at 
first an elongation of epidermal and palisade cells, does not increase in 
the number of cells. This portion becomes the bottom of the cavity, 
while the upper portion of the leaf, which surrounds the insect, greatly 
proliferates, grows upward and becomes the sides of the cavity. As 
the leaf grows, the growth of the gall proceeds, 
and at the end of twelve to fifteen days when 
the leaf is almost fully expanded, the gall has 
attained its full size and encloses the cecidial 
producer, which has increased in volume many 
times. The gall also contains several hundred 
eggs which the insect has laid. Text-figure 5 
shows such a gall, partially cut open. The one 
thing that is definitely known concerning the 
work of the insect is that it has sucked for 
fifteen days at one very small area, and that 
it has obtained enough nutriment to feed itself 
and to enable it to produce several hundred 
eggs. This sucking action suggests itself as 
the initial stimulus in gall production. It ap- 
pears to the writer that the disturbances which 
such an action would produce, such as the lowering of tensions at 
one part and the increase in another, the change in osmotic rela- 
tionships necessary to counterbalance the withdrawal of cell contents, 
are factors which are sufficient to account for the localized abnormal 
growth. 
Von Schrenk (30) produced intumescences on cauliflower leaves 
by spraying them with various copper salts. I have likewise pro- 
duced these intumescences both on cabbage and on cauliflower. 
Figure 10 shows a cross section of a cabbage "leaf with a large intumes- 
cence projecting from the lower side of the leaf. The leaf was sprayed 
with a very fine spray, only on the under side, with a solution of 
ammonium copper carbonate made up of 4.5 cc. ammonia, 0.5 g. 
copper carbonate and 750 cc. of distilled water. These hyperplastic 
Fig. 5. An opened 
gall. Showing the gall 
producer and her eggs 
filling the cavity. 
(Note the narrowness 
of the gall where the 
insect is sucking.) 
Magnified 5 times. 
