214 TUMOURS OF EUCALYPTS AND ANGOPHORAS, 



that finally, when the fusion is complete, there is no visible line 

 of demarcation. As the nodules of a flourishing pair progress, 

 they increase steadily in size, growing upwards slightly, but 

 more evidently outwards, backwards, and downwards, until they 

 meet and fuse, thus encircling the stem. Similarly the fused 

 pairs grow downwards, covering up and fusing with the portion 

 of the stem involved, until the several fused pairs have con- 

 cresced. As the hasal portion of the concrescence grows down- 

 wards, it finally encircles and fuses with the upper portion of 

 the taproot, and the proximal portions of any lateral roots that 

 it may encounter. We have an example of two seedlings grow- 

 ing so close together that the encircling tumours came into con- 

 tact and fused. If two such seedlings survived and attained 

 tree-size, they might furnish an example of apparently one tree 

 with two stems. 



The opposite and decussate arrangement of the stem-nodules, 

 corresponding to the disposition of the cotyledons and leaves, is 

 ati ideal arrangement for the production of well-balanced, sym- 

 metrical, composite, encircling tumours, provided— (1) that all 

 the pairs of stem-nodules are complete; (2) that the nodules 

 develop promptly; (3) that they grow comparatively equally and 

 uniformly, and make the necessary fusions, and the fused pairs 

 the necessary concrescences, at the right time, and in the right 

 way; and (4) that the internodes, especially the lower ones, do 

 not lengthen too soon or too much. But if one or several of 

 these provisoes fail, the final result will be correspondingly modi- 

 fied. If plenty of material is available, very suggestive and 

 instructive anomalies, of almost every conceivable kind, may be 

 obtained. 



Incomplete pairs of nodules are common. If several nodules 

 or pairs are missing, any resulting composite tumour will be 

 correspondingly smaller. A good example is shown in PI. xiii., 

 fig.2, of the E. sideroxyloii-sevias (about half nat. size). This is 

 a concrescence of the fused first pair and of one nodule only of 

 the second pair, and this, though it is included, did not make 

 much progress and contributed very little, and is still recognis- 

 able (in the specimen though not in the photograph). 



