Dec. i, 1923 
Habits of the Cotton Rootrot Fungus 407 
and the date upon which each plant wilted was written upon the tag 
attached. The progressive death rate of all of the tagged plants in the 
three sizes of spots is illustrated in Figure 1. 
It will be noted that none of the tagged plants in the outer circle 
(C plants) were attacked by the disease until after the death of all of the 
tagged plants in the intermediate circle (B plants). Although the 
plants on these circles did not die simultaneously, the sequence in which 
the different circles of plants were attacked seems to indicate that the 
centrifugal manner in which the disease spreads in alfalfa fields is not 
the result of accident. 
CONIDIAL STAGE OF THE FUNGUS 
Duggar (7) reports having observed in 1902 a circular spot or incrusta¬ 
tion of spores in the vicinity of a dead spot of cotton in Texas. He did 
not associate this with the fungus on roots of the diseased cotton plants 
until several years later, when he again examined the collected material. 
In September, 1915, he found an abundance of similar material in a field 
of diseased cotton near Paris, Tex. He was unable to find any of the 
conidial areas in the earlier stages of development, but was able to observe 
the method of spore formation by studying material from the periphery 
of the circular mass. 
During the summer of 1917 the writer observed spore masses corres¬ 
ponding to Duggar’s description in 8 of 20 infected cotton fields, three 
times under dying umbrella trees (Melia Azedarach umbraculiformis) 
and in three of eight infected alfalfa fields. In 1918, after a week of 
rainy weather in early August, the spore material was found in 10 of 13 
cotton fields where the presence of rootrot had been suspected or identified. 
A few mats of spore material were observed in infected cotton fields in 
1919, but none in 1920. During the seasons of 1917 to 1920, inclusive, 
observations were confined almost entirely to cotton fields. During that 
time no particular arrangement of the spore cushions was noted except 
that they were formed most frequently in close proximity to some recently 
dead host plant, and seemed to develop best in moist, shaded places, such 
as cracks and holes in the ground. 
During the summers of 1921 and 1922 two infected alfalfa fields at 
Sacaton, Arizona, were closely watched for the occurrence of the fruiting 
forms. Two abundant crops of conidial material appeared in all of the 
infected spots in 1921, the first following a rainy period during July 23 
to 31 and the other following a heavy rain on August 21. There were 
also two heavy crops and several lighter ones in 1922, the most abundant 
appearing after a heavy rain on August 31. The abundant crops enabled 
the writer to observe that the arrangement of fruiting bodies was not 
haphazard, but that their habit of formation was in definite circles around 
the ring of plants which had recently wilted. 
It was also noted that when conditions were most favorable the mats 
not only issued from every available crevice and hole in the surface of 
the ground, but formed upon smooth surfaces. In several spots in August, 
1922, the mats were so close together that after two days of centrifugal 
growth they presented a formation so nearly continuous as to resemble a 
buff-colored band about 18 cm. wide around the periphery of the diseased 
area (pi. 2, A). 
Thorough search failed to reveal any of the mats away from the infected 
spots, and it was but rarely that one could be found more than 30 cm. 
inside the ring of recently wilted plants. Having noted many times that 
