Sept, i, 1921 
Transmission of Some Wilt Diseases in Seed Potatoes 823 
the seed pieces were then planted on recently cleared land which had 
never grown a crop of potatoes and were given good care throughout 
the growing season. During the season notes on vine growth were made 
at occasional intervals. In the fall all the hills were dug and weighed 
separately. All hills grown from seed pieces from which known or sus¬ 
pected parasitic organisms had been isolated and a representative number 
of hills grown from fungus-free seed pieces as indicated by the cultures 
were kept for culturing in the same way that the seed tubers had been 
cultured in the spring. Some of this material was then kept for use as 
seed stock the following season, when a much larger planting on well- 
rotated land was made. The results obtained during the different 
seasons did not vary greatly but appeared to be in close accord. 
relation between tuber symptoms and occurrence of organisms 
therein 
The presence or absence of discoloration in the vascular region of the 
stem end of potato tubers has rather generally been taken (5, 7) as a 
reliable guide to the presence or absence of wilt-producing fungi, though 
for Vcrticillium albo-atrum , Petliybridge (8) has pointed out that this is 
far from being an infallible sign. Based on a study made in 1915 and 
with which the writer was associated, Edson (4) states that— 
In the materials studied, vascular discoloration of the stem-end tissues of Irish 
potato tubers was not found to be proof of the presence of parasitic fungi. Discolored 
bundles were often sterile, and fungi were frequently isolated from tissues which 
appeared normal. 
The extent to which the presence or absence of discoloration can be 
depended on as a guide to the presence or absence of wilt-producing 
fungi is of importance, for it is frequently desirable to estimate the 
amount of wilt infection in seed potatoes merely from the appearance 
of the tubers. Consequently, a further study has been made of this 
relation in several different lots of potato tubers, of which the following 
may be mentioned in detail: 
Six hundred Up-to-Date tubers grown in 1917 in hills attacked by 
Verticillium albo-atrum were cultured by the method outlined above. 
Nearly three-fourths of them (439 tubers, or 73.2 per cent) yielded 
V. albo-atrum in culture. Of these, 70.8 per cent were “browned” in 
the vascular region at the stem end, 19.6 per cent were “yellowed,” and 
9.6 per cent were “not discolored” at all. Of the 95 tubers in this lot 
which gave no organism in culture, 18.9 per cent were “browned” in 
the vascular region, 17.9 per cent were “yellowed,” and 63.2 per cent 
were “not discolored.” There were 111 tubers altogether which had 
no discoloration in the vascular region. Of these 54 per cent gave no 
organism in the cultures; 8.1 per cent gave “miscellaneous fungi” to 
which no importance can be attached, for they probably cause no disease 
of potatoes; while more than a third, 37.9 per cent, gave V. albo-atrum. 
