Shoot Axis Galls

Abstract

Structurally and ecologically, the galls on the shoot axis embrace a greater diversity and complexity of abnormal growths than on the root. Some of the essential characters of these galls may be traced to the fact that in the shoot axis we find both growth in length and growth in thickness. The development and structure of galls on the shoot axis are therefore profoundly influenced by their relation to the primary meristem and the cambial cylinder. Broadly speaking, two types of galls arise on the shoot axis, viz. the acrocecidia or the galls on the growing vegetative tip and the pleurocecidia or the galls that develop at a distance from the growing tip. The galls on the shoot axis are generally solid or hollow swellings, caused by Bacteria, Fungi, some Nematodes, a few Acarina, Homoptera, Coleoptera, Lepidoptera, Hymenoptera and Diptera. No Thysano-ptera are known to give rise to galls on the shoot axis. The relative abundance of galls caused by different organisms on the shoot axis is shown in fig. 34. In the simplest of the galls, the cecidozoa remain externally on the epidermis of the shoot.