Sept, i, 1921 
Transmission of Some Wilt Diseases in Seed Potatoes 833 
culture were small than was true in the case of any other organism. 
This relation may be further indicated by a specific comparison with the 
tubers which gave no organism when cultured. In the tubers weighing 
less than 3 ounces the percentage of all the tubers giving V. albo-atrum 
is higher than that of those giving no organism, while at 3 ounces and 
above the relative position of the two lots is reversed. 
Fusarium radicicola (fig. 3) occurred relatively more in the 2-, 3-, and 
4-ounce tubers and less in the smaller and the larger tubers than did 
Verticillium albo-atrum. F. oxysporum occurred to a less extent than the 
other organisms in the tubers weighing 3 ounces and under and more 
than the other organisms in those weighing from 4 to 7 ounces. There 
was a gradual increase in percentage of “miscellaneous fungi” (fig. 4) 
from 16.6 in the %-ounce up to 36.1 in the 1 i-ounce tubers. In the same 
range of tuber weights there was a fairly uniform decrease in percentage 
of “no organisms” isolated from 54.1 down to 37.7. Above 13 ounces 
there were so few tubers available for tabulation that the results for all 
the organisms isolated are variable. 
The two chief lessons to be gained from these data are (1) that the 
smaller potatoes should not be used for seed purposes, because they are 
apt to contain a higher percentage of wilt infection than the medium-sized 
tubers unless it is known that the plants by which they were grown 
were free from wilt, in which case, of course, the small potatoes could 
be used with safety, and (2) that wilt can not be avoided merely by the 
selection from the bin of only the medium-sized or even the larger 
healthy-looking potatoes, as even these may contain a high percentage of 
wilt infection. 
