216 PROTECTION OF WOODLANDS. 



The Oak-apple Gall-wasp, Cynips (Dryophanta) quercus folii, is 

 the principal of the various kinds of Gall-wasps that attack the 

 leaves of the Oak. It occasions the well-known large green and 

 red " Gall-apples " pendent from the lower side of Oak foliage, 

 and about the size of a cherry. 



The Oak -cone Gall-wasp, Cynips (Aphilotrix) fecundatrix, pro- 

 duces the small wooden excrescences like hop-fruits or cones 

 at the point of Oak twigs ; these cones are greenish at first, but 

 afterwards turn brown and harden. They are often collected 

 together in clusters. 



The Oak-rose Gall-wasp, Cynips (Teras) terminalis, produces the 

 large red, spongy galls at the tips of Oak twigs. These round, 

 rose-coloured, spongy galls are formed by a cluster of different 

 chambers, and are usually found at the terminal bud, where the 

 " roses " grow to the size of a potato. 



Plant-lice (Aphid*). 



The Elm-gall Aphis, Tetraneura ulmi, produces the small club- 

 like galls of the size of a pea or bean on the upper side of the leaves 

 of the Elm (and, according to Altum, only on the Ulmus campestris), 

 with which the whole of the foliage is sometimes covered. The 

 Elm-blister Aphis, Schizoneura lanuginosa, causes the large hairy 

 galls that occur on the tips of the shoots and on the foliage 

 of Elms ; during the summer these blisters contain an india- 

 rubber-like fluid in which the lice live from June till August. At 

 first the galls are green and red, but turn brown as they harden and 

 dry. The Beech Aphis, Chermes fagi, and the Ash Aphis, Chermes 

 fraxini, produce cankerous-like spots on the bark of these trees. 



alternative generation ; that is to say, winged insects develop a wingless, hibernating, 

 agamic species, which reproduces itself parthenogenetically, or without any sexual 

 intercourse being necessary, and whose brood throws back to the original form iu 

 which sexual relations are necessary for reproduction. Thus, Cynips fecundatrix pro- 

 duces C. pilosa, whose ova develop into imagines as C. fecundatrix once more ; 

 Cynips terminalis deposits ova from which C. aptera is developed, and after forming 

 galls on the roots of trees, this insect, without impregnation, lays eggs from which 

 the original C. terminalis is reproduced. This is all the more wonderful, when one 

 recollects that C. terminalis, produced at the tips of the twigs in the crown, wanders 

 away down to the roots to deposit her ova, and that the agamic form C. aptera, when 

 fully developed, migrates up to the summit of the crown, to reproduce the original 

 form there once more. Trans. 



