some features of oak gall growth. 11 



Positions Occupied. 



(a) Root, {h) Stem, (c) Leaf. (cJ) Flower. 



This section presents the same features as are found 

 in all vegetable galls. The division of the plant into 

 four primary parts affords the only simple and com- 

 prehensive scheme of classification. The student 

 desirous of following this phase of the subject is 

 referred to the author's previous work, ' British 

 Vegetable Galls,' pp. 24-30. 



Of those on roots there are two galls of distinctive 

 and definite forms, Biorhiza aptera, and Aplnlothrix 

 radicis. While the former has never been found grow- 

 ing above ground, the latter is occasionally met with 

 on small twigs springing from the tree trunk, at a foot 

 or two above the soil (see Plate XXX, div. A) . 



The most characteristic gall on the main stem, or 

 trunk of the tree, is that of Trigonaspiscrustnlis, wdiich 

 in reality is a transformed bud. Aphilothrix albo- 

 punctata is typical of an external gall on the twig, 

 and AndviciLS noduli of a gall concealed within the 

 tissues of the tw-ig. Numerous examples could be 

 cited of galls attached to the leaf. The mid-rib, its. 

 off-shoots, the under surface (mostly) of the blade, 

 occasionally the upper surface, the margin, and also 

 the petiole all have a gall or galls peculiar to them. 



The staminate flowers are attacked, a typical 

 example being Aphilofhrix (fuad I'ilineatas. Seven 

 other galls are also found on the catkins. The acorn, 

 being a subsequent development of a fertilised flow^er, 

 is included in this sub-section, the only gall found 

 within the cotyledons being that of Andricvs glandium. 



Similarity of GtRowth. 

 There is a remarkable similarity in the appearance 

 of many galls of the same or allied genera, especially 

 in galls occurring on the continent, but not as yet 

 recorded for Britain. The collector of oak galls will 

 find upon looking over a collection of European oak 



