BUD-GALLS. o-iS 



(Asperula galioides, tinctoria, &c.) as on Fir-trees. The infected parts of the shoot 



remain stunted, and white spongy cushion-shaped growths, which are somewhat 



grooved, arise at the bases of the leaves. Since the growing tissues of neighbouring 



leaves touch one another the grooves or channels form small cavities in which live 



the larvae of the gall-producing gnats (CecidoTnyia Galii and Asperulce). In the 



common Bedstraw {Galium Mollugo) these spongy growths arise, not from the 



bases of the leaves, but from the green cortex of ihe stem round the insertion of the 



leaves and lateral branches. They rise up as cushions and lobes, and several join 



together to form a sort of dome, under which the larvae of the gall-gnat dwell. The 



foliage-leaves are scarcely altered in form, and when lateral twigs arise from the 



place they also are unchanged. It not infrequently happens that short lateral 



axes terminated by flowers spring up quite unmodified above the spongy white 



cuckoo-gall. Cuckoo-galls also occur on Cruciferse, viz. on Barbarma vulgaris, 



Nasturtium palustre, sylvestre, and Sisymbrium Sophia. They are produced by 



Cecidomyia Sisymbrii, and originate principally at the bases of the flower-stalks 



half-way up the inflorescences. They look like spongy white bodies which surround 



the pedicels like the brim of a hat. As the growths from neighbouring pedicels 



meet together they roof over chambers which serve as habitations for the larvae of 



the gall-gnats. Viewed from outside the galls appear like irregular white bodies 



inserted in the inflorescence, which remind one of the fruit of the white Mulbei-ry- 



tree. 



The term cluster-gall is reserved for that type of bud-gall in which the axis is 



much restricted or stunted and covered with densely crowded leaf-structures; it 



is in the chinks and recesses between the crowded leaves of these galls that the 



insects concerned pass the whole or a portion of their lives. The animals which 



cause the galls belong to very different classes. Gnats, leaf-fleas, leaf-lice, and mites 



are the commonest varieties. The gnats only live in the galls during the egg and 



larval stages, but the others pass their whole life there. They invariably settle 



on the end of a shoot while it is still undeveloped in the bud. The axis of the 



shoot remains more or less stunted in consequence of the influence the animals. 



exercise on it and its leaves undergo fundamental alterations. The blade or sheath 



of the leaf is deepened and hollowed to afford sufficient space to the animals which 



have established themselves between them, and as these parts of the leaves touch 



one another recesses are formed not unlike those which are developed in fir-cones 



for the growing seeds. The sheathing part of the leaf is often rather thickened, 



and its succulent cells serve as food for the animals living in the gall; in other 



instances the hollowed leaf-blades are thickly covered with hairs, and this coat 



then has the same significance with regard to the insects as the felt of hairs on 



isolated leaves already described. Very different forms of galls are produced 



according as to whether the free ends of the leaves turn back or remain in contact, 



and whether the axis from which the leaves spring is more or less contracted. 



Sometimes they remind one of open rosettes, sometimes of closed balls, bunches and 



tufts, sometimes of pig-tails and witches' brooms. 



VOL. II. 85 



