182 ANNALS OF SCOTTISH NATURAL HISTORY 



floral members are often much swollen and fleshy, and are 

 fused together, the changes being greatest at the base. The 

 stamens and carpels are almost always sterile. Often the 

 parts of the flower are monstrously distorted (e.g. flowers 

 of Crucifers galled by the white rust fungus Cystopus candi- 

 dus]. Gall-mites very often cause the parts to be multiplied 

 and to become much cut, fringed, or otherwise distorted 

 green bodies. The gall-makers live between the deformed 

 parts, or within the tissues, just as in the simple galls. The 

 bud-galls show very much the same diversities in structure 

 and in surface as have been described already under simple 



galls. 



Some compound galls reach a very considerable size, 

 such as the " witch-besoms " so commonly caused by a fungus 

 on Birches, and the large irregular masses, caused by a mite, 

 that sometimes replace the inflorescence on the Ash. 



Allusions have already been made in this paper to the 

 groups of gall-makers, but a more systematic notice of them 

 may not be out of place. Those that form galls on 

 terrestrial plants in Britain belong chiefly to the groups 

 Fungi, Nematoid Worms, Mites, and Insects. Of Insects 

 the gall-makers in Britain belong to Hemiptera-Homoptera, 

 Diptera, Coleoptera, Lepidoptera, and Hymenoptera. In 

 the more recent works galls are termed Cecidia ; and they 

 are distinguished by a prefix to denote the group to which 

 the maker belongs. There is a certain amount of con- 

 venience in this usage. To indicate its method, the different 

 groups will be denoted by the appropriate names below. 



MYCO-CECIDIA.- -The galls formed by fungi belong 

 mostly to the closed type, the threads of the fungus 

 traversing the tissues of the host, and giving rise to a 

 swelling or gall, which may be localised (as in the tumours 

 on roots of Juncus bufonius caused by Endorhiza), or may 

 alter the whole aspect of the plant (as by Melanotcsnium in 

 Lady's Bedstraw). The reproductive bodies or spores of the 

 fungus may be set free only by decay of the gall (as in these 

 two fungi), or they may be formed on and dispersed from 

 the surface of the gall (as in Cystopus and in the swellings 

 of Juniper stems caused by Gymnosporangium). Hair-galls 

 and Mantle-galls are caused by certain fungi (such as some 



