INSECT galls are held to be “excrescences”; a “diseased condition of vegetable tissue”; and they are supposed to result from the “injection of a fluid,” or from some “secretion.” The student may most easily begin an investigation of galls with the dissection of those produced by the turnip weevil (Curculio pleurostigma) on the bulb of the Swede. The roots of Swedish turnips are frequently covered with hundreds of irregular spherical warts, from.03 to.75 of an inch in diameter, growing either singly or crowded together in clusters. These warts are regarded by M. Woronin (Plasmodiophora brassiae, Pringsheim's Jahrb. xi. B. p. 548) as resulting from the fungus which he has discovered to be the cause of club-rooting in cruciferous plants. I believe that on this point M. Woronin has been misled. The true clubs produced by his fungus are entirely distinct from these root-nodes. Under favourable conditions the root-nodes have been found to give rise to tufts of leaves; a fact which I can confirm by many examples presently growing in my possession. Dissection of these nodes, on Swedes, shows that they contain none of the plasma and spores which constitute the bulk of the true clubs. They are, in fact, tuberculated buds arising directly from medullary rays in the root to which they are attached. These can be traced through the enveloping parenchyma into the nodes, where they are seen to give rise to masses Of contorted and branching leaves. The nodules within the bark of the beech, hazel, and other trees, are of the same character as those on the turnip. The medullary nexus of these nodules sometimes comes straight from the centre of the tree into the node, and sometimes runs along like a cord under the outer layers of the bark, entering the node by the end.