Sept, i, i 9 2i Transmission of Some Wilt Diseases in Seed Potatoes 829 
Theformer group of tubers is the only one of the six in which a majority, 
53 per cent, of the tubers showed “no discoloration.” The nearest 
approach to this is in the group which gave “miscellaneous fungi,” of 
which, however, only 16 per cent had “no discoloration.” A little over 
one-fourth, 28.7 per cent, of the tubers which gave “no organism” were 
lightly discolored, “yellowed,” and about one-sixth, 16.5 per cent, were 
“browned.” A very small percentage were affected by “end rot” or 
were “blackened,” 1 and 0.8 per cent, respectively. 
To sum up a portion of the data in Table I, it seems clearly indi¬ 
cated that the presence of a discoloration in the stem-end vascular 
region of a potato tuber is usually though not always evidence of the 
presence of an organism there. Even distinct discoloration, though, 
does not always mean the presence of an objectionable organism, for 
only about 45 per cent of the tubers distinctly discolored contained wilt 
or other disease-producing organisms, while the other 55 per cent yielded 
either miscellaneous fungi of no apparent consequence or no organisms 
whatever. In this connection it is to be borne in mind that the cultures 
made are of course not a perfect index to the organisms present, as is 
mentioned more in detail in a later paragraph. Neither does the absence 
of discoloration always indicate the absence of a serious organism, for 
about 5 per cent of all the tubers which were not discolored gave disease- 
producing organisms when cultured. A general conclusion that seems 
to be well justified is that the variation in the degree of discoloration 
caused by any one fungus in different tubers is so large and the differences 
jn the type of discoloration caused by the various fungi are so small that 
the character of the discolorations can not be taken as a guide to what 
fungus is present or even as proof that any fungus is present. 
OCCURRENCE OR MORE THAN ONE ORGANISM IN THE SAME POTATO TUBER 
In any consideration of the occurrence of fungous organisms in the 
stem end of potato tubers the question naturally arises as to whether 
commonly more than one organism occurs at one time in the same tuber. 
In order to throw some light on this point a special set of cultures was 
made. One lot of 150 Up-to-Date tubers grown in 1917 in hills from 
plants badly wilted by Verticillium albo-atrum were cultured from all 
four quarters by the sweet clover stem method already described. In 
this case, after the tubers were treated and dried, the outer tissues at 
the stem end were cut away and the end was quartered by two longi¬ 
tudinal cuts at right angles to each other. A portion of the end of each of 
these quarters, including discolored vascular tissues whenever present, 
was then taken and placed in tubes of culture medium for incubation. 
The results, given in Table II, show that 64 tubers, or 42.6 per cent, 
gave V. albo-atrum in all four quarters, one tuber gave Petiicillium sp. 
in the four quarters included in this case under “miscellaneous fungi,” 
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