162 
Journal o f Agricultural Research 
Vol. XXIX, No. 4 
cause of the death of many of the older 
plants. There seems to be no gener¬ 
ally used common name for this injury 
to the leaves. One grower suggests 
“neckrot” and as the “neck** of the 
plant is the most noticeably affected 
part this name seems appropriate. 
The corms of plants affected with 
neckrot are not always diseased, but 
they often show very definite lesions 
on both the husks and the body of 
the corm. The infection may be so 
slight as to escape general notice, or 
so severe that the husks are practically 
destroyed and the corm covered with 
circular sunken spots. 
In its early stages the husk lesion 
is pale yellow or pale brown in color, 
circular, oval or sometimes an elon¬ 
gated streak, with unbroken tissues. 
The color becomes darker, almost 
black; the husk splits longitudinally 
and also disintegrates at its base where 
it is attached to the corm (PI. 3, 
A and B). The ragged margins have 
the texture and color of burned tissues. 
Another type of husk lesion less 
likely to be observed is a thickened 
band of tissue on the inner side of the 
husks, near and surrounding the ter¬ 
minal bud (PI. 3, H). Such lesions 
are found only by removing the husks. 
The tissues are several times the nor¬ 
mal thickness, brittle or gritty like 
charcoal, and dark brown to black in 
color. Probably this represents the 
lower margin of a severe infection on 
the leafy part of the plant which has 
extended downward to the husk as a 
continuous lesion. Forty per cent of 
a lot of corms taken from storage in 
March had this type of lesion. 
In most cases there is a direct rela¬ 
tion between husk and corm lesions, 
the corm infection occurring just be¬ 
low the husk infection. Occasionally 
lesions are found under areas of healthy 
husk, but in these cases a careful ex¬ 
amination shows some other lesion so 
situated that bacteria might pass from 
it under the husk to the place where 
the hidden lesion developed. 
Corm lesions begin as definitely 
outlined, pale yellow water-soaked, 
circular spots. The epidermis shows 
no visible injury and all the tissues are 
firm. The color deepens, varying on 
corms of different colors, from light 
yellow-brown to dark brown or almost 
black. The epidermis remains intact 
over some lesions, but usually it be¬ 
comes split or broken. Eventually the 
corm lesion becomes a shallow depres¬ 
sion surrounded by a definite and 
somewhat elevated margin (PI. 3, G). 
These depressions are usually only 
2 to 6 mm. in diameter, but, when 
numerous, they coalesce and form large, 
irregular sunken areas. The pits do 
not extend deeply into the flesh of the 
corm and are rather easily removed, 
leaving a clean, saucer-shaped cavity 
lined with healthy cells. 
Gladioli are subject to several dis¬ 
eases which produce corroded spots or 
pits on the surface of the corms, and 
although those caused by Bacterium 
marginatum are usually quite char¬ 
acteristic, it is realized that injuries 
due to other agents may produce lesions 
having a general appearance not unlike 
those which numerous isolation and 
inoculation experiments have proved 
to be caused by Bacterium marginatum. 
The name scab is a good descriptive 
term for these lesions on the corms. 
This name occurs frequently in the 
literature of gladiolus disease and it is 
probable that in many instances the 
spots described were due to this 
bacterial infection. Some illustrations 
by Wallace {11) and others closely 
resemble the spots caused by Bacterium 
marginatum. 
A rather striking phenomenon is the 
copious gummy exudate from the corm 
lesions. At first colorless, it changes 
to yellow-brown or dark brown, and 
when dry is brittle and shiny like var¬ 
nish. The diseased husks are glued to¬ 
gether and to the corm by this exudate 
and sometimes even the surrounding 
soil becomes impregnated with gum and 
forms a mass closely attached to the 
corm (PI. 3, E and F). Just under each 
such mass of soil are the lesions from 
which the exudate flowed (PI. 3, G). 
It has not been determined whether 
this exudate is due to the action of 
Bacterium marginatum alone or aided 
by the various secondary organisms 
which attack the injured tissue. No 
gum exudes from leaf lesions or from 
quite young corm lesions. The exudate 
gives a positive reaction for sugar, 
which perhaps explains the presence of 
the many secondary organisms. 
RELATION TO HOST TISSUE 
Microscopic examination of sections 
of fresh and of stained material of leaf 
tissue shows that the bacteria are ac¬ 
tive only in the parenchyma. Bacteria 
have not been found in the vessels, but 
eventually in a diseased area the ves¬ 
sels are filled with a reddish-brown 
substance. The walls of vessels are 
browned and occasionally show brown¬ 
ing even beyond the limits of the dis¬ 
colored parenchyma. 
Bacteria enter through the stomata 
but it has not been proved that this is 
the only mode of invasion. Stomata 
