MISS 5. LONGMAN ON THE DRY-ROT OF POTATOES, 135 
IV. The stems did not fall down until some time after they were quite 
dead, but, as they were very shrunken at the base, this was probably 
owing to their having been very thoroughly earthed up. 
Smith and Swingle (04) give a figure showing the distribution of disease 
in their plots at a certain date (July 27th). "The distribution is curious as 
the disease does not appear to have spread from a centre of infection, but 
diseased plants appear scattered singly or in small groups throughout the 
plots. In many cases not all the shoots from one “seed-potato” were 
attacked ; some remained perfectly healthy after others had been killed, 
The distribution of the disease in the Reading plots, on August 1st, 1907, 
was strikingly like that described by these authors. 
The potatoes at Reading were grown on a freshly broken pasture, to 
which no manure had been added, and which was therefore thought to be 
free from disease. The seed-potatoes also appeared to be free from disease 
up to the time of planting. 
Some of the Heading plots were planned for spraying experiments, and 
were sprayed with * Bordeaux mixture" during the summer. Other plots 
were devoted to Infection Experiments: some of the seed-potatoes of one plot 
and the ground of another plot being inoculated with blue Fusarium at the 
time of planting. 
On August Ist diseased plants appeared to be evenly distributed throughout 
all the plots, even the plants from the inoculated seed-potatoes showing no 
higher percentage of disease than those from the uninoculated sprayed or 
control plots. 
What the source of infection is, is unknown. It would be natural to 
suppose that the fungus gains an entrance into the sprouting tuber or the 
damaged root from the soil. But the occurrence of the disease in plants 
grown on a freshly broken pasture which had not borne a potato-crop for 
many years, suggests either that the fungus has a wide-spread saprophytic 
existence in the soil or that it is commonly present in the potatoes themselves. 
Bernard (02) has made the interesting suggestion that the tuber of the 
potato is itself a hypertrophy due to the irritant action of Fusarium. 
Without claiming the results of the Reading experiments as confirming this 
hardy hypothesis, they would seem to offer some slight support thereto. 
On this view, a nicely balanced struggle between fungus and potato 
results in a healthy tuber, whereas the balance, slightly disturbed in favour 
of the fungus, results in the diseased plant. In any case К. Solani appears to 
be a somewhat erratic parasite and often incapable of infecting actively 
growing potatoes, although, as has already been shown, it attacks the 
Stored and dormant tubers with much greater ease. 
