Robinson and Walkden. — A Critical Study of Crown Gall . 323 
4 
27 . Smith, Erwin F. : Further Evidence that Crown Gall of Plants is Cancer. Science, N.S., 
June 23, 1916. 
28 . -: Mechanism of Tumour Growth in Crown Gall. Journ. Agric. Research, 
iii. 165, 1917. 
29 . -: Embryomas in Plants (produced by Bacterial Inoculations). Johns Hop¬ 
kins Hospital Bull., xxviii. 277, 1917. 
30 . -: The Relations of Crown Gall to other Overgrowths in Plants. Mem. 
Brooklyn Bot. Garden, i. 44S, 1918. 
31 . -: An Introduction to Bacterial Diseases of Plants. Philadelphia and 
London, 1920. 
32 . -: Effect of Crown Gall Inoculations on Bryophyllum . Journ. Agric. 
Research, xxi. 593, 1921. 
33 . Swingle, D. B., and Morris, H. E.: Crown Gall Injury in the Orchard. Agric. Expt. Sta. 
Bozeman, Montana, Bull., cxxi, 1918. 
34 . Toumey, J. W. : An Enquiry into the Cause and Nature of Crown Gall. Agric. Expt. Sta. 
Arizona, Bull., xxxiii, 1900. 
35 . Walkden, H.: The Isolation of the Organism causing Crown Gall on Chrysanthemum 
frutescens in Britain. Ann. Bot., xxxv. 137, 1921. 
36 . Winkler, H.: Ueber die Umwandlung des Blattstieles zum Stengel. Pringsheim’s Jahrb. f. 
wiss. Bot., xlv. 1, 190S. 
EXPLANATION OF FIGURES IN PLATES V AND VI. 
Illustrating Messrs. Robinson and Walkden’s paper on a Critical Study of Crown Gall. 
PLATE V. 
Fig. 1. Typical crown galls produced on Chrysanthemum frutescens by inoculating cut surfaces 
of the stems with B. Himefaciens. a and b are galls four months old ; c is a younger gall produced by 
inoculating an axillary shoot which arose near to the first gall ( a ). Natural size. 
Fig. 2. Radial longitudinal section of a gall (four months old) on the cut surface of a stem. The 
callus-like growth is shown, and also the extension of the influence leading to an abnormal increase 
in diameter of the stem below the gall, x 5. 
Fig. 3. Radial longitudinal section of a similar gall to that in Fig. 2, five and a half months 
old. a, woody gall-tissue ; b, actively proliferating gall-tissue ; c, layers of necrosed cells. X 1^. 
Fig. 4. Median longitudinal section through the apex of a shoot of Chrysanthemum frutescens , 
showing leaf-rudiments and parts of young leaves of various ages. The leaf (/.) has just differentiated 
the first protoxylem element of the leaf-trace and is at the stage of development usual when inocula¬ 
tions result in secondary galls on the leaf similar to those seen in Fig. 12, s.g. 1, s.g. 2, s.g. 3. x 50. 
Fig. 5. Portion of transverse section of young stem of Chrysanthevmm frutescens at the level of 
the first distinctly visible internode below the growing-point of the shoot, x 75. 
Fig. 6. Film of Bacterium tmnefaciens stained with carbol fucnsin. x 1250. 
Fig. 7. Radial longitudinal section of stem of C. frutescens , showing the cut surface nine days 
after inoculation. The dark staining of some areas and of cell-walls near the surface is due to bac¬ 
teria in the protoxylem vessels {px.), pericycle fibres (pf), and in some intercellular spaces (z.s.). 
x 75 - 
Fig. 8. Radial longitudinal section of stem similar to that seen in Fig. 7, fifteen days after 
inoculation. Shows the region of the pith adjoining the vascular bundle and the progression of the 
disturbance outwards from the bundles across the pith. Elongated cells fr.) with tracheide-like 
thickenings are appearing. x 65. 
Fig. 9. Radial longitudinal section of stem similar to Figs. 7 and 8, fifteen days after inoculation. 
Bacteria present in protoxylem ( px .) and in a line of intercellular spaces ( i.s .) in the cortex. This 
line of infection, which is the dark region immediately to the left of the large-celled cortical tissue in 
the photograph, forms a centre for pathological disturbance, x 50. 
