191 ON CERTAIN SHOOT-BEARING TUMOURS OF EUCA-LYPTS AND ANGOPHORAS, AND THEIR MODI-FYING INFLUENCE ON THE GROWTH-HABIT OF THE PLANTS. By J. J. Fletcher and C. T. Musson. (Plates iv.-xxvi.) The Eucalypts, representing about 230 recognised species, contribute one of the dominant, phanerogamic elements to the Australian flora. They are an assemblage of plants remarkable in many ways, widely distributed over an entire continent, ex-tending also to the circumjacent islands; and now acclimatised to some extent in other countries. One of the astonishing things about them is the liability of the seedlings of so many species to shoot-bearing galls or tumours of an uncommon type. Their specially distinctive characters result from a fortuitous combination of some simple, natural, and favouring conditions present in quite young seedlings. Firstly, they originate in the axils of the cotyledons only, or, in addition, in a few pairs of leaf-axils successively above these, where the buds are, as paired but at first independent, proliferating outgrowths of cambium-tissue; and, as a rule, the outgrowths, or the axillary stem-nodules, as we may call them at this stage, succeed in taking possession of the dormant buds, and incorporating them in the stem nodules. This is how the latter, as well as the composite tumours to which they may give rise, come to have buds or shoots. (Secondly, the young seedlings usually have opposite and distichous leaves; and, correspondingly, the stem-nodules are also opposite and distichous; but as, under favourable conditions, the latter grow faster than the stem thickens, the paired nodules meet and fuse, and the fusions then encircle the stem. Thirdly, as a rule, the first and second internodes do not length too much or too soon to permit of the concrescence of the fused
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