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 



