266 PATHOLOGICAL FORMATIONS. 
produced in quantitatively very considerable amounts, a case of 
symbiosis ' (cohabitation) is thus presented here, of beings be- 
longing to two different series, though, since the one lives chiefly 
at the expense of the other, this borders closely on parasitism. 
These formations are very remarkable from the fact that a plant 
does service for an insect and constructs for the latter its 
dwelling place. 
‘Since insects of different classes (Hemiptera, Diptera, Hy- 
menoptera) participate in the production of insect-galls—and 
only these interest us here— it is impossible to make any state- 
ments of general application regarding these gall formations, 
which occur upon plants of all the families of phanerogams.’ 
Their shape, like the nature of the irritation which produces 
them, is extremely variable. 
Only those galls which are rich in tannin are of technical 
importance, and these are also our best sources of tannin. The 
oaks, especially, furnish many valuable galls.* 
The galls of Asia Minor (or galls in a general sense) are pro- 
duced by the puncture of the ovipositor of the female insect of 
Oynips galle tinctorie Olivier (a Hymenoptera) in the young 
shoots of Quercus lusitanica Lamarck. The female insect, de- 
veloped in the hypertrophic tissue from the egg deposited 
therein, afterwards bores for itself a passage and escapes from 
the gall, by which it was sheltered during one of its phases of 
life. 
The so-called Chinese and Japanese galls, on the contrary, 
are produced by the female Aphis sinensis (a Hemiptera) in the 
younger shoots and leaf-stalks of Rhus semialata Murray. In 
these galls, which are mostly very large, the numerously intro- 
duced eggs become developed as plant-lice, pass through succes- 
1 Sur with, and zevr to live. 
*Compare especially, Frank, ‘‘ Handbuch der Pflanzenkrankheiten.” 
_ ®The galls which are employed technically and pharmaceutically 
have been very excellently described by Hartwich (Arch. d. Pharm., 
21, 1883, p. 820); compare also Wiesner, ‘‘ Rohstoffe des Pflanzenreiches,” 
Vienna, 1873, pp. 846, with numerous illustrations. 
