List of the Insect Fauna of the County. 103
the growth."11 Hofmeister observed the same principle when
he maintained that the growth of the gall is due to the fact
that it encloses an active living grub;12 but he has over-
looked those very obvious circumstances in which we find the
galls fairly formed and often well grown before the larva-state
of their legitimate inhabitants is reached. Here we fall back
on Hartig, who had already clearly demonstrated the absolute
growth of the curious pedunculate eggs of the Cynipidae and
other terebrant Hymenoptera.13 Dr. Hollis gave a quotation
from Guibourt, which I here include,14 relative to the com-
mensalism between the active life of the gall and of the
gall-maker; and then continues, "With some reservation I
accept the theories of Hofmeister and Guibourt, with regard
to the origin and growth of the gall-nut, but I must introduce
a third element into their formation, which appears to have
been somewhat overlooked by these writers, and that is, the
active growth of the plant itself."15 This all-important
element had probably been understood, still it needs enun-
ciation. It is most certainly a fact that a gall is never
produced, except on those parts of a plant which are in
active growth and in full receipt of the sap-flow. It may
also, I think, be taken as a fact that the more active the
11 'Flora of Berwick-upon-Tweed,' ii. 108.
12 'Die Lehre von der Pflanzenzelle,' p. 634. (Leipzig, 1867).
13 'Wiegmann's' Archiv fur Naturgeschichte,' iii., p. 151, pl. iv., 1837.
Germar's 'Zeitschrift fur die Entomologie,' ii., p. 179 (1840), and iii.,
p. 327, pl. i., figs. 5, 6 (1841). Also consult 'Over de Legboor van
Aphilothrix radicis, Fabr." By Dr. M. W. Beijerinck, in the 'Tijdschrift
voor Entomologie,' vol. xx., pp. 186—198, plates 11 and 12; 1876—7.
14 "Une autre observation qui est commune aux autres galles, c'est que
tant que l'insect y est enferme, la gaile du chene tauzin offre une couleur
rougeatre et verdatre, et une surface luisante qui indiquent qu'elle
participe a la vie de l'animal; tandis qu'apres sa sortie, elle prend une
couleur terne et grisatre et semble mourir." 'Histoire naturelle des
Drogues simples,' 1849 ; ii., 278.
15 In a note on insect gall buds, Mr. A. Stephen Wilson, of Aberdeen,
under date May loth, 1879, thus writes to 'Nature' (vol. xx., p. 55):—
"The insertion of the ovipositor brings a medullary ray into action,
producing a tuberculated bud, and it is only the bud which the larva
feeds upon. The growth of a bud is an intelligible cause of the growth
of a gall, but we can infer nothing from the injection of a fluid."