104 
NATURE’S CRAFTSMEN 
sort of long petiole or footstalk six to ten times 
the length of the egg itself. It is jabbed into the 
leaf by the gall-fly’s long, curious-shaped, egg- 
laying tool, and by some means not clearly un¬ 
derstood the misused leaf is made to transform 
itself into a nursery for the gall-fly baby. Once 
upon a time it was thought that a poisonous liquid 
was deposited with the egg, but presently it was 
noted that no change was to be observed in the 
leaf until after the egg hatched. Therefore, now 
it is supposed that the larva itself secretes a liquid 
which causes the abnormal growth. This liquid 
is not capable of producing an entirely foreign 
growth unaided, you understand; it simply stim¬ 
ulates the cells which are the most active in grow¬ 
ing and subdividing, and the plant does the rest. 
“ Galls are queer things, and show a wide range 
of form. Moreover, all galls are not made by 
gall-flies. Some beetles and caterpillars, a few 
Chalcis flies, and certain mites and scale insects 
produce galls. But usually when galls are men¬ 
tioned it is the product of the gall-flies that is 
thought of; perhaps because for so many years 
the galls of the dyer’s oak, a product of the gall¬ 
fly, were imported in large numbers to be used 
in the manufacture of ink. 
“ Gall-flies of every species seem to be par¬ 
ticularly fond of the oak. They pierce its shoots, 
its twigs and leaf-stalks, and even the mid-rib of 
