LEVINE: STUDIES ON PLANT CANCERS—IV 239 
duced crown galls which averaged 1.5 cm. while inoculation in 
the axils with similar quantities of the same emulsion gave an 
average growth 1.8 cm. for twenty-two plants. The result here 
really suggests a summation of the stimulus from the bacterial 
organism and the natural budding tendencies of the tissues in 
the leaf axil if indeed, there is not an actual bud with more or 
less active growth tendencies in the axil of every leaf. 
When the size of the crown gall in the axil of a leaf of anormal 
plant is compared with that in the axil of a leaf of a decapitated 
plant it is found that the axillary crown gall is larger (see TABLE 
Emulsion I). A comparison of the size of the crown galls on 
stem internodes with those in the axillary buds of decapitated 
stems produced in each case by equal quantities of the same 
dilution shows much larger crown galls for the decapitated plants; 
(study TABLE, Emulsion IV). It appears that the size of the 
galls produced by equal quantities of similar or identical sus- 
pensions of Bacterium tumefaciens inoculated depends upon the 
location of the inoculation. The midvein of a leaf shows the 
smallest crown gall reaction; while the axil of a leaf of a de- 
capitated stem shows the largest growth. This was of course 
already implied in the general comparison of galls from different 
parts of plants. 
RELATIVE VIRULENCE 
It is a well recognized fact in general old cultures of patho- 
genic bacteria are less virulent than young cultures. The 
cultures used in these experiments were subcultures of Bacterium 
tumefaciens (hop strain) sent to this laboratory by E. F. Smith 
in 1917. These had been kept in culture and used in my former 
experiments. When the present experiments were started 
cultures varying from two to one hundred and ninety days old 
were available. The latter were too dry to warrant any attempt 
at use. Cultures two days old were made up into various dilu- 
tions (Emulsion VI) of which 6a is the undiluted culture drived 
by scraping the media upon which the organisms were growing. 
The crown galls which resulted from inoculating the stem inter- 
node with this culture showed an average of 1.6 cm. in diameter. 
Emulsion 3a which is an undiluted culture of Bacterium tume- 
faciens twenty-one days old grown under the same conditions as 
Emulsion VI also gave crown galls of an average diameter of 1.6 
