2l0 TUMOURS OF EUCALYPTS AND ANGOPHORAS, 



shoot at the back, a little to the left of the stem, has six nodules, 

 of which four are visible — the first pair not fused; the second 

 pair dislocated, probably due to a pair of leaves becoming alter- 

 nate; one only of a third pair, and one of a fourth pair, with a 

 shoot. Another tumour-shoot, hidden in the photo, also has a 

 good pair. 



These three seedlings show, then, that axillary nodules may 

 develop on tumour-shoots which develop in the ordinary way, or 

 on second-growth shoots, whose development has been accident- 

 ally stimulated. 



The Nodule- Shoots. — Until the morphology of the seedlings, 

 and the histology of the nodules and composite tumours have 

 been investigated, one can attempt to interpret macroscopic 

 characters only with reserve. The shoot-bearing character of 

 the nodules is due to the fact that the axillary outgrowths take 

 over and incorporate thedormant buds (or the bud-forming tissue), 

 which, otherwise, would be smothered. But so many shoots 

 sometimes develop on a single nodule, or on a fused pair, that we 

 are inclined to think that the nodules sometimes carry away 

 bud-forming tissue, rather than simply differentiated buds; and 

 that the stimulus which is responsible for the proliferation of the 

 cambium to form the nodules, may also cause the bud-forming 

 tissue to proliferate, and spread. 



On the other hand, sometimes the growing nodules fail to take 

 over the buds. Three good examples are shown in the two 

 Stringybark seedlings in PI. xii. Another is shown on the stem 

 of the seedling of fig.l of PI. xiv. Also two others in the re- 

 fractory seedling, c2 of PI. x.; for the two futile nodules of the 

 third pair, and the two branches just above them, belong to the 

 same pair of axils. There are some other examples on the re- 

 markable seedling in PI. xviii., particularly the pair of which 

 one is numbered 4. In such cases, the bud and the nodule 

 develop separately; if the bud perishes, the nodule is left stranded 

 on the stem. If both develop successfully, it is noticeable that 

 the nodule is usually on the outer side of the branch in the ex- 

 ternal angle between the branch and the stem, fused to both. 

 This suggests that, as the nodule develops on the outside of the 



