BUD-GALLS. 543 



spongy gall, red-cheeked on the sunny side but pale elsewhere, which is produced 

 on the tips of the branches of the Oak by the gall-wasp Dryoterus terminalis, and 

 looks very like a potato in shape. The leaves are only represented by small ill- 

 defined knobs and ridges, just as in the potato. To this class of galls belongs 

 also that to which the term " nut " is popularly applied, and even in commerce, the 

 name has been transferred from this to the whole of the first group of compound 

 galls (bud-galls). The "nut" is produced on the Oak by Gynips calicis as an 

 angular and irregularly-grooved gall which originates at the end of a flower axis, 

 and the cupule formed of several bract-scales as well as the ovaries are concerned 

 in the growth. This class of galls also includes the irregular blunt swellings on 

 Aspen twigs (Populus tremula), which are caused by the larva of a beetle (Saperda 

 populnea), and in addition the many-chambered woody "canker cushions" as large 

 as a nut which are produced on the branches of Willows by Nematus medullaris. 



The gall shown in fig. 364 ^, which arises on various Oaks {Quercus pedunculata, 

 sessiliflora, pubescens) by the action of the gall- wasp, Aphilothrix geTumce, may be 

 selected as a type of leafy bud-galls. It resembles the cone of a Hop or Larch, 

 and is developed from a foliage-bud. It has a much-abbreviated swollen axis, whose 

 tissue separates into an inner and outer gall, beset with numerous dry, brown lan- 

 ceolate hairy scales having the form of bract-scales. Bud-galls which are covered 

 with green foliage-leaves are produced by the gall-wasp Andricus inflator on the 

 Oak, but they are more commonly met with on herbaceous plants, e.g. by Urophora 

 cardui on Girsium arvense, by Diastrophus Scabiosoe on several Knapweeds {Gen- 

 taurea alpestris, G. Badensis, G. Scabiosa), by Aulax Hieracii on various Hawkweeds 

 (Hieraoiwm murorum, sylvaticv/m, tridentatum, &c.). Usually the foliage-leaves 

 are stunted, and not infrequently the blades of some of them are quite obliterated, 

 so that the gall in that region is only furnished with scaly leaf-sheaths. A Sage 

 growing in the Isle of Crete so often bears leafy bud-galls resembling a small 

 Quince-apple, produced by a species of Aulax, that Linnaeus called it Salvia pomi- 

 fera. The stem of this Sage is swollen out like a ball, and the spherical mass, 

 covered with a gray felt of hairs on the exterior, is surmounted at the top with a 

 group of small wrinkled leaves, which look like the persistent calyx of a Quince- 

 apple. The best known and most widely distributed of these forms, found on the 

 Hawkweeds named above, consist of knob-like swellings of the stem. The larval 

 chamber is situated inside the enlarged pith, the ring of vascular bundles, which has 

 undergone much shifting, forms the protective layer, and the cortex of the afiected 

 region of the stem forms the cortical layer of the gall. The epidermis is densely 

 covered with hairs. 



Leaving the galls which consist of modified foliage-buds, we pass on to such as 

 consist of metamorphosed flower-buds. They arise from flower-buds in which small 

 gall-gnats have laid their eggs. The larva hatched from the egg lives in the cavity 

 of the ovary, or. in one of its loculi when there are several, and this space, therefore, 

 becomes the larval chamber. The corolla, which envelops the ovary in the flower- 

 bud, remains closed, like a cap on the top of the larval chamber. The calyx becomes 



