Robinson and Walkden.—A Critical Study of Crown Gall. 301 
According to his view the presence of the bacteria, in the initial stages of 
the disease, provides the stimulus, which is then continued by the stimulated 
but uninfected cells behaving as parasitic cells similar to cancer cells. He 
has also studied another tumour growth on beet, from which it is not clear 
Bacterium tumefaciens can be isolated, and has successfully transferred this 
tumour between red and yellow forms of Beta , but there is little indication 
of any true infiltration of tumour-tissues in this case. 
Kuster ( 11 ) states that in secondary galls caused by B. tumefaciens 
conclusive proof of the infiltration of tumour-tissues described by Smith has 
not been obtained, and suggests that it is more likely the effects are produced 
by the movement of the gall-producing organisms through the tissues of the 
host plant. He also denies that the stem-like structure of leaf-galls is 
derived by the growth of tissues from the stem into the leaf and mentions 
that such structure is frequently seen in other galls. 
Peklo ( 17 ) produced tumour-strands and secondary galls similar to 
those described by Smith by the inoculation of the developing capitula of 
Helianthus. 
Friedemann and Magnus ( 3 ) have emphasized the fact that crown galls 
are special irregular developments of wound tissue resulting from the 
infection by B. tumefaciens , and they hold that Smith’s figures are not 
decisive regarding the intrusive growth of tumour-tissue. These two 
authors, on the grounds of cultural and serological characters, at first 
thought that certain strains of bacteria isolated from intestinal and some 
other diseases of man were identical with B. tumefaciens . Of the many 
strains so isolated only one proved capable of producing crown galls on 
plants. Friedemann ( 5 ), however, showed later that this organism was 
invariably in symbiosis with B. proteus, and, since it was only isolated from 
faeces and not from diseased tissues, that there is no real ground for 
ascribing to B. tumefaciens any pathogenicity to man. 
Magnus ( 16 ), in a later paper, showed that there is no evidence in 
favour of the opinion expressed by Blumenthal and Hirschfield (1) that the 
pathogenic properties of B. tumefaciens can be transferred to saprophytic 
bacteria commonly associated with it. 
Riker ( 18 ), in a paper which, so far as we know, has not been published 
in full, states that B. tumefaciens can live in soil for at least a year, and that 
he has obtained microscopic evidence, derived from primary and secondary 
galls on the raspberry, indicating that the bacteria live in small quantities 
in the intercellular spaces of the host. He also states that under certain 
conditions he found the organism able to travel through the vascular 
bundles. 
Levine ( 13 , 14 , and 15 ) has studied the origin of leafy growths on 
Bryophyllum inoculated with B. tumefaciens , the behaviour of crown gall on 
Ficus elastica , and the effect of the previous health of beetroot upon the 
