80 THE AUSTRALIAN NATURALIST. 
tissues or organs which are serviceable to the plant. We can- 
not, in the case of gall formation, speak of a symbtos that Is a 
joint life of two organisms in which both parts obtain equal 
advantage from one another. It is only in quite exceptional 
cases that the gall-producer brings true services to the shelter- 
ing plant.” y 
Formerly it was supposed that when an insect deposited its 
eggs in the tissue of a plant it injected an irritant fluid at the 
‘same time, which latter, in its turn, caused the formation of 
the growth we call a gall. In some cases (notably Gall-flies— 
Cynipide) the fluid, if of any service at all, is probably to 
keep the puncture, caused by the ovipositor, open, because if 
the wound healed over, the egg would in all probability be 
crushed. Experiments made by Huropean entomologists have 
shown that when an egg is extracted from the bark before it 
has had time to hatch, no gall-growth has resulted. How, 
then, is the gall formed? The answer is—by secretions 
discharged by the larva, together with the local irritation 
caused by the creature gnawing the tissue that surrounds it, 
and it is this that gives shape to the gall. 
European oak-galls are the best known. Some occur upon 
leaves, and others on the terminal buds. These, known 
as ‘‘Oak Apples,” are caused by some species of Cynips, or 
gall-wasp. In former times an abundant growth of oak 
apples was supposed by country folk to herald a good season 
and bountiful harvest—a safe surmise, as the same condition 
was responsible for both. 
In commerce, the gall most frequently used was obtained 
from stunted oaks, Quercus infectaria, « species common in the 
Levant. The products from this was ink and dye. A large 
number of galls was used annually in this industry; indeed, 
upwards of 1,000 tons of these oak apples used to be imported 
into England. They were the work of larvee of a species of 
Oymips, and were round, about the size of a marble, and 
covered with small tubercles. The most valuable came from 
Syria and Smyrna. On the borders of the Dead Sea there is 
another species of stunted oak, from which are obtained galls 
of considerable size, and famous in history as “ Apples of 
Sodam,” ‘‘Mad Apples,” or‘ Dead Sea Fruit.” These are 
caused by the punctures of Gall Gnats. Many curious galls 
are found in Japan, large quantities of which are used in the 
arts and medicine. 
In Europe the typical gums, Quercus (oaks), appear to be 
the most affected by galls; and the same remark applies here, 
in Australia, to our typical Hucalypts, or Gum trees. It is 
upon the latter that our largest and most striking forms 
occur. 
Corvorrers.—There is nothing very striking about the galls 
constructed by beetles. Several species of Buprestide form 
