612 BACTERIAL DISEASES OF PLANTS 



surface (Figs. 438, petiole, and 448 A, blade). Very frequently 

 the proliferation is abundant only over the main ribs of the leaf- 

 blade or in their vicinity (Figs. 438, 441, 442, 443) but not always 

 (Figs. 427, 433Z, and 446 4 .). Sometimes it is restricted to the 

 apex of the shocked leaf. This apical development I have 

 observed 5 or 6 times. On the internodes it may be strikingly 

 one-sided (Figs, 429C, 435, 4365, 4440, quite uniformly distrib- 

 uted (Fig. 429^4, B), or more on the upper or lower end, the latter 

 depending apparently on the condition of the neighboring in- 

 ternode, i.e., on whether it is proliferous. Thus, frequently, I 

 found one internode proliferous throughout, but only the apex 

 of the next below it, or only the base of the one next above it 

 (see Table II). When the phyllomania is one-sided, involving 

 two internodes, the leaf midway on the free side of the stem is 

 itself free (Fig. 435-/V), while the leaf next below it and the one 

 next above it (those on the proliferous side of the internodes) 

 are both proliferous. This I explain, as already suggested, by 

 supposing more water to have been drawn from one side of the 

 stem than from the other. On the nodes, the chief seat of pro- 

 liferation is around the stipule-scars, which would seem to be 

 places where the plant is least well protected. 



28. In addition to being stunted, the shocked leaf-blade may 

 be variously twisted and distorted (Fig. 440j), owing to ex- 

 cessive proliferation from its main ribs, the tissues being crowded 

 downward, since most of the shoots are from the upper surface 

 and they must have room to grow. In this way the ribs may 

 become abnormally thick, corky and cracked open in many 

 places, quite as if parasitized. 



29. The adventive leaves in this begonia are not mirror 

 images of the parent but quite normal in orientation (except 

 positively geotropic on under surfaces) and, except for fusions, 

 only abnormal in number, size, shape and vitality, because they 

 are crowded and starved. I have seen one case in which that 

 part of the dorsal surface of a leaf-blade directly over the petiole 

 was fused its whole length to the dorsal surface of another blade, 

 the petioles also being fused, but the blade-wings free (Fig. 

 448 C) ; other fusions are common. 



The abnormalities (Fig. 452) observed on these adventitious 



