144 



KNOWLEDGE. 



[August 1, 1893. 



is a one-celled structure; but it is naturally many- 

 chambered, and normally provides accommodation for a 

 family of gall-flies, irrespective of parasites, wbicb of course 

 also occur in it. This is a springtide gall, tbe fly issuing 

 at tbe end of May or tbe beginning of June. Tbe galls, 

 bein<^ fully formed by tbe end of May, and being just at 

 that°time by no means inelegant objects, were formerly 

 in considerable request as buttonbole decorations on tbe 

 29tb of May, " Restoration Day," wbence tbeir popular 

 name of "King Cbarles's apples." When tbe galls have 

 yielded up tbeir rigbtful occupants tbey still do not cease 

 to be useful. Tbose resplendent green beetles, tbe rose- 

 cbafers, find tbem out in June, and devour tbe softer parts, 

 leavin<' tbe bard oval cells exposed to view m a cluster at 

 tbe end of the twig. But even if the softer part be not 

 eaten off by insects, it still disappears, flakmg away piece 

 by piece, so that if the galls are looked for m the winter, 

 only the clusters of hard cells will be found. From these, 

 however, parasites often issue, sometimes even as late as 

 tbe second year. . 



Another gall-fly, called Dnjophnnta scutdlarts, makes 

 spherical galls on tbe under side of tbe oak leaves ; these, 

 when young, bear considerable resemblance to the marble 

 galls, which, as we have seen, are tbe produce of quite a 

 different insect. When mature, however, they could not be 

 confounded ; tbe present galls become yellowish, and finally 

 red like a ripe fruit on the side turned towards tbe sun, 

 whereas tbose of Ci/nips Kollari become dark brown and 

 woody. Their situation, too, on the Intres instead of the 

 twigs, helps to distinguish them ; the flies, moreover, 

 mature later than the generality of tbose from the marble 

 galls. When these galls are fully grown they are about 

 the size and shape of cherries, and this, coupled with their 

 rosy sides, has acquired for tbem the name of "cherry 



galls." , 



Yet another globular gall may be found pretty frequently 

 on oak leaves, tbe so-called " berry gall," smaller than the 

 last, semi-transparent, and very juicy. Save for its colour, 

 it reminds one of a currant, and hence, when found grow- 

 ing on tbe pendant catkins of the male flowers of tbe oak 

 (for it occurs in this way as well as on leaves) it gets the 

 name of "currant gall." The name of its founder is 

 SpritlHV'ister hacan-nm. The growth of this gall is remark- 

 ably rapid ; only about three weeks elapse between tbe first 



appearance of the 

 gall and tbe emer- 

 gence of tbe fly. 

 It is only in May, 

 therefore, that we 

 should expect to 

 meet with the 

 galls, for after 

 the escape of tbe 

 insect tbey shrivel 

 up and soon dis- 

 appear. If any are 

 to be seen later 

 tbey will be found 

 to be inhabited 

 by parasites. 



One of the most 

 remarkable of oak 

 galls is that known 

 as the " artichoke 

 gall" (Fig. .'5), in- 

 habited by ^/)/iiio- 

 tliri.r iifiiiiiKr. Un- 

 til a section of the gall is made, and the insect foimd therein, 

 it seems impossible to believe that we have before us any- 



FlO. 5.— Artichoke Gall of Oak Tree. 



thing more than a normal vegetable production. Ga Is can. 

 hardly be regarded in any other light than as patbologica 

 features in the life-history of the plant, tumours as it 

 were, resulting from a deranged condition of the tissues; 

 and yet in such instances as the present there is no 

 trace of any irregularity of form, or shapelessness and 

 malformation, such as we should expect m a diseased 

 product, but all is beautifully symmetrical and regular, 

 the parts being arranged according to the ordmary laws 

 of plant structure. Of course there are galls which are 

 obviously abortions and monstrosities, and which greatly 

 disfi-ure tbe plant on which they occur, but that is not 

 the case with any of those we have yet considered and 

 least of all with the artichoke gall. It is of a pale whitish 

 or yellowish-green colour, reminding one very forcib y ot 

 an artichoke flower in miniature. It is in reality a modified 

 bud but still one modified without distortion ; and there- 

 fore there are a number of leafy scales overlapping one 

 another perfectly regularly, and making a rather stumpy 

 conical body, Uke the head of a thistle. On turning back 

 these leaves, an oval object is seen standing erect in the 

 centre ; this is hollow, and is the abode of the grub of the 

 sail-fly, hence it is the really important part ot the gall, 

 the rest being merely accessories. About the end ot 

 Au<^ust this hollow chamber falls to tbe ground, and 

 remains there throughout the winter, tbe insect issuing 

 from tbe gall during tbe next spring. 



A large woodv gall is sometimes found on the roots ot 

 the oak' tree, just where tbey leave tbe trunk, and theietore 

 only sUghtly' below the surface of the ground, f bis is 

 occupied by a gall-fly called after the locality m which the 

 gall occurs, Aphihthnr r.dirh. In form it is something 

 like an oak-apple, but it is much harder and more fibrous ; 

 moreover, it is usually much larger, being indeed tbe largest 

 of our British galls, and attaining sometimes the size ot a 

 man's fist. Like the oak-apple, it is tenanted by large 

 numbers of tbe flies, each inhabiting a bard-walled oval 

 chamber. The colonies are sometimes extremely extensive, 

 givm- one some idea of the high degree of fecundity often 

 attained by gall-flies. Westwood records having obtained 

 as many as eleven hundred specimens of the riglittul 

 occupant from one gall of this kind, which was about five 

 inches long by one-and-a-half broad. Tbe flies appear in 



"^^Galls have been for a long time known to science, 

 as indeed, from the conspicuousness and attractive 

 appearance of some of them, might have been expected 

 Theopbrastus, a Greek philosopher who lived about thi;ee 

 hundred years before Christ, tbe author of one oi the 

 earliest botanical treatises extant, mentions them ; and 

 Dioscorides, a writer on medicine, who lived some four 

 hundred years later, discusses their medicinal virtues in 

 a work which became one of tbe standard medical trea ises 

 of the Middle Ages. In consequence ot tbe tanniii tliey 

 contain, tbey were valued for their astringent properties, 

 and were largely used as a remedy for affections ot the 

 mucous membrane of the mouth, and other sumlar com- 

 plaints. By tbe ancients they were always treated as 

 purely vegetable products, and the true nature ot the 

 LnnJction between the plant, the gall and tbe insect 

 does not seem to have been suspected till comparatively 

 recent times. Even Bacon speaks of oak-apples as an 

 " exudation of plants joined with putrefac ion. i lo 

 great difficulty about them was always fe t to be the 

 presence of an insect inside a portion ot a plant, without 

 any apparent means of entrance ; this greatly puz/.led he 

 learned, and led to many curious conjectures as to he 

 possible method of its introduction. It was evident that 

 the insects were batched in the place in which they wtio 



