A Dry Rot of the Irish Potato Tuber 
19 
In these the growth of the fungus at first is appressed, appears 
white in color, and the edge of the colony is marked by a fluffy, 
white, aerial mycelium. This fluffy edge is characteristic of cul- 
tures thruout their entire development. The central part of 
the colony produces conidia first on aerial hyphae, which soon 
collapse and allow the conidia to fall on the hyphal mat and give 
it a pink color. If secondary germination of conidia sets in. the 
whole mass is covered by another mat of aerial hyphae. which 
often do not go over to conidia formation, and consequently the 
culture looks more white than it normally does. When the cul- 
ture has been under favorable conditions of light and moisture, 
an enormous number of conidia are formed, which fall down to the 
substratum, so that we get concentric rings of heaps of hyphae 
and conidia, which look like series of embankments (PI. XXII). 
The whole colony appears powdery after two weeks' growth. In 
the agar a very firm plectenchyma is formed, which sets up 
tensions, pulling the mass into wrinkles as it grows older. No 
stroma-like or sclerotial bodies are formed. 
On some potato tubes masses of mycelium which were black 
or dark blue in color were formed if the oxygen supply was cut 
down. According to Appel and Wollenweber the appearance of 
sclerotia need not be considered as a taxonomic character. They 
are by far not as pronounced in Fusarinm tuberivorum as they 
are in Fusarium orthoceras according to Appel and Wollen- 
weber's and the writers' observations. 
THE MYCELIUM. 
In this organism we have to consider a complex of hyphal 
threads. Under proper conditions the hyphae fragment termi- 
nally into colonies of cells, usually called spores or conidia, which 
may be made up of from one to eight cells. That we have colonies 
is indicated by the fact that these spores break up into oidia when 
put into unfavorable conditions such as are realized when the 
fungus is grown on beef bouillon or in distilled water. On beef 
extract the mycelium itself can be made to fragment interca la- 
rally into such colonies. Such fragments, however, do not show 
the end differentiation which the end cells of the usual colony 
do. At times, in tube cultures, and in distilled water, the myce- 
lium fragments terminally or intercalarally into round, thick 
walled, simple, or compound colonies which usually are smooth 
and full of oil. On raw potato plates such colonies with spiny 
walls were noted and these can be called chlamydospores. 
Under other conditions the mycelium vegetates as such with- 
out spore formation, especially if the temperature is low and if 
there is an abundance of food. The same condition was realized 
