412 
Journal of Agricultural Research 
Vol. XXVI, No. 9 
The periods of most active fruiting usually lasted only two or three 
days unless followed by continued rainy or humid weather. A rainy 
period began on July 23, 1921, and continued for about 10 days. During 
this period the mats developed in such abundance as to cover almost the 
entire surface of the ground around the circles of dying alfalfa plants 
in some fields near Sacaton. Jorden (2) and Shantz and Piemeisel (7) 
have called attention to the influence of weather conditions, especially 
moisture, on the production of fruiting bodies in fungus fairy rings. It 
would appear that the organism associated with rootrot in Arizona is no 
less sensitive to this influence in its processes of fructification. 
REESTABLISHMENT of alfalfa plants in rootrot areas 
In studying the behavior of rootrot in alfalfa fields, the writer observed 
that a considerable number of alfalfa plants recover even after the por¬ 
tions above ground have succumbed to the rootrot attack. When the 
circles, which begin with one dead plant and spread in all directions, 
have attained a diameter of 3 or 4 meters, various weeds and grasses be¬ 
gin to appear in the center of the bare circle and spread outwardly (pi. 
2, B), rarely reaching within a distance of 1 meter of the rim of dying 
plants during the time in which the disease is most active. The plants 
which appear most frequently in the alfalfa rootrot circles near Sacaton 
are Capriola dactylon, Holcus halepensis , Echinocloa colona , Chenopodium 
murale, Trianthema portulacastrum , Leptilon canadense, Leptochloa im- 
bricata , Physalis angulata. Starting at about the same time as the weed 
growth, a number of alfalfa plants near the center of the circle begin to 
send out new growth. When water is applied through rainfall or irri¬ 
gation it often happens that a great number of these supposedly dead 
plants begin to leaf out, and, along with the weeds, revegetate the central 
portion of the bare circle. When one of these plants is lifted from the 
ground, it is often found that a piece of taproot, about 15 or 20 cm. long, 
has remained alive, just below the crown from which a number of lateral 
roots have extended, and brought new life to the plant (pi. 3, B). In 
rare instances plants are found which show the entire taproot rotted 
away and a large number of lateral roots branching out directly under 
the crown. In several circles the number of reestablished plants were 
counted, and it was found that they ranged from none in small circles, 
of about 2 meters diameter, to 38 per cent in larger circles, about 20 
meters in diameter. During the winter months circular rootrot spots 
are often observed whose entire areas are occupied by several concentric 
circles of reestablished plants interspaced alternately with bare circles 
where no alfalfa growth was renewed. It is evident that the rings of 
plants represent those which had died just before a summer cutting of 
hay which was immediately followed by the customary irrigation. The 
bare rings doubtless represent the location of plants which died when 
the soil was comparatively dry, and to which no water was applied for 
a considerable time. 
MANNER OF RECURRENCE OF ROOTROT SPOTS DURING SUCCESSIVE 
YEARS 
Scofield (6), from charting rootrot spots in rotation experiments at 
the San Antonio Experiment Station for 7 years (1912 to 1918), has 
shown that while the disease in cotton fields usually occurs in well- 
defined spots in one season it may not recur in the same places in the 
