Robinson and Walkden.—A Critical Study of Crown Gall . 305 
the former case vve have frequently observed, at stages from twelve to 
fifteen days after inoculation, the ends of gall tracheides extending to the 
outer surface of the gall. The uninoculated control shoots treated as 
cuttings develop a small amount of parenchymatous callus (Text-fig. 3), 
Text-fig. 2. Series of radial longitudinal sections through lower ends of inoculated cuttings at 
intervals: A of 6 days, B of 12 days, C of 15 days, and I) of 18 days after inoculation. Areas of 
active-tissue proliferation indicated by dotting. Regions of vascular bundles originally entered by 
bacteria indicated by darker lines near the ends of the former. x 9. 
Tlxt-fig. 3. Series of radial longitudinal sections through lower ends of control, uninoculated 
cuttings at intervals : A of 6 days, B of 1 2 days, C of 18 days, and D of 21 days after planting. The 
vascular bundles are indicated, and the amount of callus proliferation is shown at the ends of these 
bundles, c — callus ; r = roots. x 9. 
whilst the cut surfaces at the upper ends of shoots exposed to air become 
dry and at most show a very few divisions of the cells adjoining the surface, 
a bulge of callus never being formed. Even in the control cuttings the 
amount of callus produced is never great and, so far as we have observed, is 
always purely parenchymatous in character, the proliferation slowing off 
after roots are developed behind the callus (Text- fig. 3, C). Text-fig. 3, D, 
X 1 
