FLORIDA STATE HORTICULTURAL SOCIETY. 
I17 
minute, egg-shaped spore (seed) at the tip 
of each branch. When a spore falls on 
the moist surface of a leaf it pushes out a 
slender, colorless thread which soon enters 
the leaf, and if the weather conditions are 
favorable, it soon completely penetrates 
and kills the leaf. It usually takes about five 
days from the time the spores germinate 
until a new crop of spores are formed. This 
explains why the disease spreads so rapid¬ 
ly. The tubers of infected fields may, or 
may not, rot. This depends largely upon 
soil and weather conditions. This rot is 
worst on heavy soils. The fungus has 
no winter spores. It is believed to pass 
the winter in the tissue of the tubers, con¬ 
sequently too much care cannot be ex¬ 
ercised in selecting clean, healthy seed. 
Thoroughly sprayng the plants with Bor¬ 
deaux mixture will hold the disease in 
check. 
Fnsarium Oxysporiniu (Schlechtendal). 
Dry Rot —Attacks all parts of the po¬ 
tato plant below ground. The first in¬ 
dication of the disease is a change in the 
appearance of the leaves, which take on a 
lighter green color and roll up, followed 
by a gradual drying up and premature 
death of the plant. However, if the plants 
are not attacked until they have about com¬ 
pleted their growth these early symptoms 
are often lacking. The upper part of the 
shoots become flabby, droop and die, 
usually taking on a dark brown color. 
When infected tubers are first dug they 
appear sound, but while they are stored 
the fungus gradually works inward, fol¬ 
lowing the vascular ring. (This ring 
soon takes on a brown or black color). 
The fungus usually gains entrance at the 
stem end. Black streaks extending from 
the stem into the flesh is a reliable 
symptom of this disease. Infected ends 
rot and shrivel, and because of this pecu¬ 
liarity the disease is often spoken of as dry 
end rot. The hyphae (feeding threads) 
which occur abundantly in the diseased 
tissue, often appear on the surface of 
the tubers in dense, white tufts. These 
soon bear small oval spores (seeds) and 
later a larger, curved, septate form. If 
these spores fall on the moist, injured sur¬ 
face of tubers and plants, they germinate 
and develop new points of infection. 
This is a wide-spread and destructive 
disease. It is a difficult matter to find a 
lot of seed which is not more or less in¬ 
fected with it, and it is not uncommon to 
find as high as 25 per cent of our seed com¬ 
pletely rotted by it. Frequently tubers 
which are healthy when they are cut, are 
completely rotted by this fungus beforethe 
plants reach the surface of the ground. 
This is especially noticeable when the ger¬ 
mination of the seed is checked by un¬ 
favorable weather conditions. In such 
cases the fungus gains entrance through 
the cut surface. The rotting of the seed 
in various sections of the State during the 
past winter was due largely to the work of 
this organism. In a number of fields which 
came under our observation, as much as 
60 per cent of the seed was rotted by this 
fungus after it had been cut for planting. 
The infection in most cases was largely 
due to carelessness in mixing diseased 
seed pieces with healthy ones. The spores 
falling on the cut, moist surface soon ger¬ 
minated and invaded the tuber. The 
planting was followed by a spell of cold 
weather which retarded the germination of 
the seed, thus enabling the fungus to 
consume the tuber before the young plants 
reached the surface of the ground. In 
fields where the planting was followed by 
more favorable weather conditions, the 
stand was much better, still many of the 
