198 TUMOURS OF EUCALYPTS AND ANGOPHORAS, 



If the shoot-bearingj axillaiy nodules of Austialian Eucalypti 

 are caused by parasitic soil -organisms, under natural conditions, 

 then they seem to be comparable with the five cases of " leafy 

 tumours" [on Geranium, Pelargonium (two), Rose, and Carnation] 

 due to axillary infection by the organism causing Crown- 

 Gall under natural conditions cited, by Dr. Erwin Smith. 



Were it not that, by a fortuitous combination of circumstances, 

 the axillary stem-nodules are able to fuse in pairs, the fused pairs 

 to concresce, and the re-inforced, composite, stem-encircling 

 tumours thus enabled to incorporate roots and so last for some 

 considerable time or even permanently, both the nodules, and 

 any shoots they might develop, would be short-lived and abortive: 

 as they actually are in refractory seedlings; and as the shoots on 

 the lower pairs of concrescences also are. 



They are not exactly comparable with the embryomas pro- 

 duced by Dr. Erwin Smith's inoculations in leaf-axils and grow- 

 ing-points. But the circumstances and conditions in the two 

 cases are not parallel. Erwin Smith's experiments were mostly, 

 but not entirely, carried out with soft-tissued plants, which 

 responded promptly; the organisms were introduced by needle 

 inoculations right into the tissues of the plants, causing profound 

 disturbances; and the inoculations were made in upper axils. 



But in the natural inoculations in the lower axils of the young 

 seedlings of Kucalypts, which furnish some of the most \alued 

 hardwood timbers, we are inclined to think that the organisms are 

 confined to the outgrowths, and the encircling tumours to which 

 they give rise, and probably do not invade the tissues of the seed- 

 lings. The tumours do not kill the seedlings, or even seriously 

 damage their tissues. 1 hey are a drag on the normal develop- 

 ment of the plants, especially so when shoots do not develop, and 

 bv interfering with the water-supply, and also by iheir shoots 

 preventing the development of the normal branching. In the 

 Mallees, so much water is intercepted by the tumours, that the 

 seedling-stem is dwarfed; and, by the persistence of the shoots, 

 the growth-habit is permanently distorted, so that the plants are 

 prevented from realising their potentialities as trees. The seed- 

 ling-stem may possibly be sometimes crowded out and got rid of. 



