‘ DISEASES OF CULTIVATED PLANTS 433 
in them black masses of a species of fungus (Vermicularia) whose relation to the 
disease is undetermined. At digging time it was found that in addition to grub 
injury, the tubers were very generally infected with the markings of the dry-rot 
fangus in the conducting tissues. Sections of the stem end showed brownish 
discolorations of the vessels, and occasionally tubers showed marked invasion 
by the fungus. Tubers collected elsewhere sometimes showed these discolorations 
of the vessels extending half the length of the tuber. Injury by grubs favored 
infection. ‘ 
Following these discoveries quite thorough studies were made of potato con- 
ditions in the state, and it developed that the fusarium blight prevailed in local 
fields throughout the entire potato growing area. While some growers had ob- 
tained fine crops in spite of limited infection other growers had suffered seriously. 
4 5 6 
Fig. 83. Potato tubers attacked by Dry-Rot Fusarium, showing sections near the stem-end of 
healthy (No. 1) infected potato tubers. (Nos. 2-4) This infection may be easily discovered by cross sec- 
tions made with a sharp knife, and sections from sterilized tubers give cultures in Petri dishes. At 
times the discolorations extend to the middle of the tuber. )From a photograph by T. F. Manns). 
One grower in Summit county, who had succeeded very well in 1908 had such 
serious loss of crop from fusarium blight that he was led to attribute it to spray 
injury since blighting and dying went on in spite of the spray treatment. Inves- 
gation showed that his entire area was very badly infected with this fusarium. 
He was advised of the fact and warned against using infected seed or immediate 
planting of infected land. It developed also that northern grown seed showed 
up. quite satisfactorily. On further examination it developed that the seed from 
Red River Valley and from parts of New York and possibly parts of Michigan 
was nearly free from infection by this fungus. It was also developed that seed po- 
tatoes stored in cellars have sometimes given much less satisfactory return than 
seed from the same field stored in outdoor pits. This would seem to be explained 
by the known fact that (Fusarium oxysporum) the dry-rot fungus, makes slow 
progress at low temperatures, that is 42° or below. This disease presents a real 
problem in potato growing for the year of 1910, and interpreting the results of 
1908 in light of the experiences of 1909, one is led to infer that the disease then 
prevailed and accounted in part for the general early dying of potato tops.. 
