1020 
Journal of Agricultural Research 
Vol. XXIV, No. 12 
when the yellow or red pigment, depending on the variety, is fully 
developed. At this time the plants have one to three thin, papery outer 
scales which are intensely colored. These cover the succulent scales and 
extend up over the neck of the bulb, where they frequently connect with 
their respective green portions of the tubular leaves or *‘top,*' although 
the latter may have disappeared by this time. Following these outer 
scales upward from the base, we find that the pigment ceases very ab¬ 
ruptly above the bulb, leaving the neck sheathed largely by uncolored 
tissue (PI. i). Toward the end of the growing season there is among 
colored varieties a tendency toward some pigment reduction in the outer 
scales, especially in the portions above the soil line. This becomes 
more noticeable when bulbs are allowed to remain in the ground for a 
prolonged period after they are mature and ready for harvest. 
When the disease appears early, several weeks before harvest, a few 
fruiting bodies of the fungus are occasionally found on the dead outer 
scales of colored varieties. These scales, usually only slightly pigmented, 
slough off before harvest. Practically all of the subsequent infection on 
colored varieties is confined to the outer sheath at or just above the neck 
of the bulb. This tissue, like the lower portions of the outer scale, is 
practically dead previous to harvest, but little or no pigment is present. 
This condition is illustrated in Plate i, which shows one set each of red, 
yellow, and white varieties, all taken from the same field a few days 
before harvest. It is to be noted that the disease has become general on 
the bulb of the white variety, while in the yellow and red varieties it is 
confined to the uncolored sheath of the neck. In onion-set fields, this 
condition of infection at the neck very often becomes general on colored 
varieties if there is sufficient rainfall and high relative humidity to bring 
about dissemination of the fungus and infection. The intensely colored 
portions of the outer scales rarely show signs of the disease. The infec¬ 
tion at the neck is largely sloughed off at harvest, leaving little or no 
sign of the disease in storage. On white varieties, as stated above, the 
fungus usually covers the entire bulb and continues to invade the fleshy 
scales, causing a gradual shrinkage. 
INOCUI^ATION EXPERIMENTS WITH BUEBS 
The field observations reported above have been confirmed by plot 
experiments in which the plants were grown on well-infested soil or were 
inoculated three to four weeks before harvest with spore suspensions of 
the causal organism. In these experiments a number of varieties of each 
color were included. Table I gives a list of the varieties used and the 
dates of the trials. These trials confirm the general field data in that the 
white varieties all appeared to be highly susceptible, while the colored 
varieties were highly resistant to the disease. In the case of the latter 
group, where infection did occur it was present in small amounts and 
usually at the neck of the bulbs where the pigment was less intense. 
Occasionally the outer pigmented scales bore some fungus stromata, but 
usually the latter were associated with a lessening of pigment due to one 
cause or another. In other instances, invasion of the fleshy scales was 
noted where they were exposed to the soil, due either to splitting or to 
partial disintegration of outer scales when the bulbs were not harvested 
promptly. This observation is in accord with the following experi¬ 
mental evidence which shows that when the fungus is applied directly 
to the fleshy colored scale, invasion readily takes place. 
