FORMS AND ORIGIN OF GALLS. 13 



gall remaining inert until the early spring, when 

 growth sets in. In texture we find equal variety. 

 They may be perfectly smooth, or rough and reticu- 

 lated. From the perfectly glabrous galls of Neuro- 

 terus baccarum there is every transition, from the 

 shortly-haired galls of Neuroterus lenticularis to the 

 galls of Andricus ramuli, which are enveloped in enor- 

 mously long hair. A few galls exude a glutinous 

 secretion (Andricus Sieboldi, A. glutinosus). In Rho- 

 dites we have galls with four or five stout spines, and 

 others where the gall is thickly spined all over. In 

 herbaceous plants the galls usually take the form of 

 strumous swellings, as also in Bubus. 



The colour of the galls is, as a rule, at first with 

 many, e. g. Andricus radicis, Gynips Kollari, white, or 

 white with pink, the latter apparently being deve- 

 loped by sunlight, and is probably altered chlorophyll. 

 The catkin galls are greenish, getting brownish with 

 age. Other galls remain always green. 



Every part of the plant is attacked by the gall-flies. 

 The roots, the trunk, the leaf, either on its surface, 

 edge, or veins and midrib, the cf and ? flowers, and 

 the fruit are all utilised. As a rule each form con- 

 fines its attack to one particular part of the plant, 

 but there are exceptions to this. Thus the gall of 

 Neuroterus baccarum (spring form) is found on the 

 leaves and on the <$ catkin, Andricus radicis on the 

 roots and on the trunk. We know also of cases 

 where different plants are used. At least two Euro- 

 pean species are polyphagous. Biorhiza aptera has 

 been found at roots of beech (Curtis), firs (Masters), 

 vine (Magretti), and Diastrophus rubi has been re- 

 corded as having been found on the galled tops of 

 Pteris aquilina. Aulax hieracii, besides attacking 

 various species of Eieracium, occurs on Gistus and 

 on Triticum. Apart from the case of B. aptera, no 

 species of Gynips, Andricus, Dryophanta, Biorhiza, 

 and Neuroterus are found on plants other than the 

 oak. 



