1050 Marvels of the Universe 
Photo by) [H. Bastin. 
FEMALE GALL-WASP 
This is the ‘‘winter female’’ without wings, which 
emerges from the root-galls, and by her egg-laying causes 
the production of the Oak-apple. 
as a gall. But scientific observers have found that 
although the gall-insect actually injects fluid into 
the wounds which she makes in the bud, she does 
this either to provide a lubricant for the working 
of her ovipositor, or as a varnish to seal up the 
injury. The fluid, in fact, has been proved to be 
innocuous. We are left to assume, therefore, that 
the presence of the eggs, and subsequently the 
gnawing of the tiny grubs, are the factors which 
determine the growth of the gall. It must be 
remembered that the eggs are invariably laid in 
actual contact with what botanists call cambium 
or meristem tissue—+z.e., the layer of delicate cells 
which, by rapid multiplication, bring about the 
phenomenon which we call “the growth of the 
plant.” These cells are known to be highly sensi- 
tive, and it is not, therefore, unreasonable to 
suppose that their behaviour is influenced by the 
proximity of foreign bodies—viz., the eggs and 
young grubs. The gall, in fact, is due to an 
irregular and excessive growth of the plant tissue, 
and we may regard it as a kind of non-malignant 
tumour. The harm done to the oak is not serious, 
being limited to the destruction of one bud; but the gain to the insect is very great indeed, for 
the Oak-apple is at once the nursery and the feeding-ground of the little family of grubs. Each 
grub lies in a chamber surrounded by the spongy tissue of the gall, bathed in the sap upon which 
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Photo bu] [H. Bastin. 
FEMALE GALL-WASP. 
The winged female that emerges from the Oak-apple, 
and lays her eggs in the roots of the Oak, thus causing the 
production of root-galls. See page 1052. 
it feeds. It grows rapidly, changes to a pupa, and 
in June becomes a perfect “ fly,’ which bites its 
way to the surface of the gall, and so escapes 
into the air and sunlight. 
Strange to say, the insects which emerge from 
the Oak-apple are totally unlike their parent— 
the ant-like creature which laid the eggs in the 
oak bud. Apart from minor differences, they 
have wings, while their ranks are made up of 
males and females, whereas the wingless winter 
generation consists entirely of females which are 
endowed with the mysterious power of partheno- 
genesis, or virgin reproduction. In a word, the 
life-cycle of the Oak-apple insect exhibits that 
remarkable phenomenon which naturalists call 
“alternation of generation ’’—a phenomenon that 
has nullified the old-time theory that like in- 
variably produces like. Moreover, the habits of 
the winged insects which come from the Oak- 
apple are quite different from those of their pro- 
genitors. After pairing, the females resort, not 
to foliage buds, but to the roots of the oak. 
They work their way beneath the soil, and 
