Robinson and Wa/kden.—A Critical Study of Crown Gall. 307 
Sometimes after three days, but always at six days after inoculation, the 
abnormal cell-divisions, leading to gall production, have commenced. The 
cells, particularly of the parenchyma, adjoining the regions of the vascular 
bundle and the cortex entered by the bacteria, show enlarged nuclei, and 
themselves either merely enlarge or more frequently become subdivided 
into smaller cells which maintain a meristematic character. 
After nine days the influence of the presence of the organisms has 
extended laterally from the vicinity of the vascular bundles, both into the 
cortex and into the pith, and by this time the consequent increase in 
diameter of the end of the shoot is becoming evident (Text-fig. 1, B). PL V, 
Fig. 7, shows a portion of the upper end of such a shoot after nine days ; 
the dark patches seen indicate the position of bacteria on the inoculated 
surface, in the intercellular spaces adjoining this, and also in the vessels 
and in the tissues of the phloem and pericycle. 
PI. V, Fig. 9, which is a portion of a similar shoot fifteen days after 
inoculation, shows how the passage of the bacteria into the intercellular 
spaces of the cortex, some distance from the surface, may result in centres 
of disturbance around which gall-tissue develops by the subdivision of cells. 
In the Chrysanthemum, however, so far as we have observed in these 
inoculations, the distance the bacteria extend either along the vessels or 
intercellular spaces is never more than about 2 mm., whilst in Nicotiana , as 
will be shown below, the bacteria may extend for a distance of some inches. 
At the age of the galls shown in PI. V, Figs. 8 and 9, while a proportion 
of the proliferating cells continue to be meristematic, others lose their con¬ 
tents and become transformed into tracheide-like cells, with characteristic 
reticulate or pitted thickening which later becomes lignified. In the pith 
these gall-tracheides (PI. V, Fig. 8) extend at right angles to the bundle, and 
appear progressively from the bundle towards the centre of the pith, being 
formed from the products of division of pith-cells. 
We must regard the effects so produced in the pith as resulting from 
influences diffusing out laterally from the vascular bundles, for when vertical 
needle-prick inoculations into the pith of cut shoots similar in age to those 
used for the other inoculations were made, beyond a slight subdivision or 
cells surrounding the needle track, no marked production of gall-tissue, 
including tracheides, was observed. 
Later stages in the development of the gall are seen in PI. V, Figs. 2 
and 3, and Text-fig. 1, C, D, and E. The whole structure of galls in these 
stages is remarkably similar to the callus masses which develop on cut shoots 
of woody twigs (such as Pop?dus) when kept in moist air. The gall-tissue 
extends completely across the pith, and the vascular bundles and cortex on 
either side are considerably.widened out by the gall, much of which forms 
irregular woody tissues with intervening parenchyma. The galls are now 
more or less hemispherical in shape ; there is a distinct zone of meristematic 
