Perhaps the most interesting of the Oak's pensioners to the woodland rambler will be the varied forms of gall on different parts of the tree. There is the so-called Oak-apple, of uneven surface and spongy to the touch, which certain people still wear on May 29th, in honour of Charles II.; the well-rounded hard Bullet-gall of _Cynips kollari_, the Artichoke-gall of _Cynips gemmae_, the Spangle-galls of _Neuroterus lenticularis_, so plentiful on the back of the leaf, and the Root-gall of _Biorhiza aptera_. All these galls are abnormal growths, due to the irritation set up by the Gall-wasps named, when they pierced the young tissues in order to lay their eggs in them. Where any of these galls are perforated it may be known that the Gall-wasp whose grub fed within has flown, but where there is no such perforation the grub is still within, feeding upon the flesh of the gall, or in the chrysalis stage, awaiting translation to the winged condition. Several Oaks of foreign origin are also grown in our parks and open spaces; among them the Holm Oak (_Quercus ilex_) whose evergreen leathery leaves have toothed or plain edges, and occasionally the lower ones develop marginal spines, whence its name of Holm or Holly Oak. It is notable for retaining its lower branches, so that its appearance, as Loudon remarks, "even when fully grown, is that of an immense bush, rather than that of a timber tree." It is a native of Southern Europe and North Africa, and appears to have been introduced about the middle of the sixteenth century. It usually attains a height of from twenty to thirty feet, but occasionally specimens are seen up to sixty feet. It has a much thinner, more even bark than that of our native Oak, and of a black colour. The long brown acorns do not ripen until the second year. [Illustration: _Pl. 6._ Holm Oak.] [Illustration: _Pl. 7._ Acorns of Turkey Oak.] The Turkey Oak (_Quercus cerris_) is a much larger tree, attaining to similar heights to our British Oak, but easily distinguishable by its more pyramidal outline, and its attenuated leaves. The lance-shaped lobes of these are unequal, sharp, and angular; and the footless acorn-cups are covered with bristly or mossy-looking scales. The acorns, which are small and exceedingly bitter, rarely ripen till their second autumn. The whole tree--trunk, branches, and twigs--is of straighter growth than _Quercus robur_. It is a native of Southern Europe and the Levant, and was introduced about one hundred and seventy years ago.