A Dry Rot of the Irish Potato Tuber 
45 
CONIDIOPHORES. 
In Fusarium orthoceras the conidophore is generally only 
a sterigma-like branch arising laterally from a hypha and cut- 
ting off conidia from its end. Sometimes a conidiophore with 
a tri-sterigmate structure is found. Ordinarily as it is found on 
potato and as it grows on agar and on potato plugs, Fusarium 
tuberivorum shows the same structure of conidiophores that 
Fusarium orthoceras does (PI. XXVI, fig. 1). In the cold, how- 
ever, the tri-sterigmate conidiophore appears. On stems and on 
raw potato plates when quite dry, we find compound conidio 
phores in which each sterigma-like branch of the first order can 
branch into three others and thus three or four tiers are formed, 
presenting a complex compact mass resembling the structure of 
the conidiophores of Fusarium rubiginosum (PI. XXVI, figs. 2 
and 3). 
CHLAMYDOSPORES. 
In these cultures chlamydospores. which may be borne ter 
minally or intercalarally, have appeared. Most of these are round 
and smooth and heavily stored with oil. On beef-bouillon agar 
and in distilled water the mycelium and spores can be made to 
fragment into oidia. Each of these cells is quite thick walled, 
hyaline, full of oil, and capable of germination. Their size gen 
erally is 6-12 x 8-12 mu (PI. XXVII, figs. 1 and 3) . 
The writers have found single cells and compound cells 
which are thick walled, ochre colored, and spiny, only rarely in 
water and in potato tubes. On a raw potato plate numerous 
chlamydospores appeared only once in a series of several hun- 
dred cultures. The fungus has been grown by others for a year 
or so in this laboratorv and not once did chlamvdospores appear 
during that time (PI. XXVII, figs. 2, 3, 4, 5. f>,' 7, and 8). 
It is apparent that with this character we have a variable 
thing, so variable that under proper conditions the whole fungus 
can be made to go over into the oidia form and look like a 
Oladosporium. Dry air and low food supply seem to favor the 
development of these oidia and chlamydospores. The size of the 
chlamydospore generally is 8-12 x 10-12 nm. 
SPORE MEASUREMENT. 
The measurements of spores taken from various cultures in 
all stages of development show a surprising uniformity, the only 
exception appearing in those spores which were grown at low 
temperatures, they being a trifle wider than the ordinary spores. 
On agar the following are the averages: 
