LEVINE: STUDIES ON PLANT CANCERS—IV 233 
He washed seed samples and calculated the spore content of the 
washings by counting the spores of a given quantity of washings 
against red blood cells. While Cobb was the first to count 
spores of parasitic diseases of plants Bolley (1902) first suggested 
the use of the centrifuge in removing the spores from seeds for 
microscopic determination. Heald (1921) took up the work of 
Bolley and Cobb and devised new methods for calculating the 
number of spores of smut per wheat grain. He planted seeds 
with a known spore number and then estimated the degree of 
smutting in the crop. Heald also infected wheat with known 
quantities of smut spores and determined the degree of infection 
in the crop. For example, he determined that 0.5—3 gm. of 
air dry spores per hundred wheat grains gave maximum smutting. 
Heald contends that there seems to be a gradual increase in the 
percentage of smut in a crop with an increase in the number of 
spores carried by each grain. He does not believe that in- 
fection of wheat “7 bunt can be accomplished by a single 
spore. 
My earlier studies on crown gall in sugar beets (Levine, 1921) 
dealing with the effect of soil conditions on the health of the host 
and the size of the crown gall produced by inoculation have led 
me naturally to the problem of what the quantity of bacteria 
used in the inoculum has to do with the size of the crown gall. 
This study was started simultaneously with the study of the 
effect of soil conditions on the size of the crown gall in 1920 and 
was continued in the following year, 1921. While the results 
are not complete, the data obtained so far, seem to be of suf- 
ficient interest to warrant this report. 
METHODS 
During the month of May 350 tobacco seedlings sent from 
Virginia, varying in height from 6 to 10 inches, were set out in 
uniformly treated soil under similar light and moisture conditions. 
Toward the latter part of July and early August the plants 
were inoculated with Bacterium tumefaciens. Eight different 
emulsions of four different ages were used as inocula. These 
cultures were grown under uniform laboratory conditions and 
ona — which consisted of 50 gm. beans, I |. water, 15-20 
rar agar. Enough of the medium was poured into 150 cc. 
Pema? flasks to cover the bottom toa depth of rcm. The 
