A Dry Rot of the Irish Potato Tuber 
15 
Appel and Wollenweber's monograph carries a full bibli- 
ography and no attempt is made to duplicate it here. It is evi- 
dent that if our knowledge of the taxonomy of the genus has been 
in chaos prior to 1910, the knowledge of the pathological condi- 
tions which these organisms bring about has been in no better 
condition, because the work done cannot be linked to any definite 
organism and because no reliable isolation and inoculation ex- 
periments have been made in many cases. 
OCCURRENCE OF THE ORGANISM. 
The organism has repeatedly been isolated by the writers 
from potato tubers affected with dry rot. If the rot has pro- 
gressed only slightly, a sunken, wrinkled spot appears on the 
surface of the tuber and usually no exterior signs of the fungus 
are visible. As the rot progresses the fungus area increases and 
finally the potato presents a shrunken, wrinkled appearance. 
Later in the progress of the disease small tufts of hyphae, which 
are pink in color, may appear on the surface but these should not 
be called sporodochia (PI. I). 
If one cuts into a partly rotted tuber, a part of the tuber will 
be found perfectly sound and the other part, which borders on the 
spot, made up of disintegrated potato tissue, of hyphae and 
conidia. The potato tissue has a brownish color and is mealy 
and dry. Here and there large cavities appear, due to rents, 
which are formed as the cells shrink away from each other, and 
which are often filled with hyphal masses of a whitish color (PI. 
X, fig;. I). When such a potato is cut open and exposed to light 
the fungus soon takes on a pink color. 
If potatoes infected with this organism are kept in rather 
moist conditions, or if the outer crust is not ruptured, the 
fungus may eat out the entire contents of the tuber, leaving 
merely the cork layer (PI. X, fig. 1). Often pure cultures can 
be obtained at first trial from such a tuber, because of the fact 
that the fungus leaves behind itself a crust of hard, dry starch 
as it makes inroads on the tissue, thus shutting out other fungi. 
If the wound is open, secondary infections occur, and often 
bacteria and other fungi, such as Penicillium and Verticilliitm. 
are found with the Fuftarium. Frequently a wet rot precedes the 
dry rot if the proper causal bncteria get in (PI. II). If an in- 
oculation is made by cutting the surface of a tuber and plncing 
the inoculum on it, thus Jetting the fungus work down and form 
a crust as it goes, secondary infection rarely sets in. If, however, 
an inoculation is made by puncturing the skin, thus leaving a 
hole, bacteria generally get in. 
