Dec. i, 1923 
Habits of the Cotton Rootrot Fungus 
411 
It will be noted that in 15 of the 24 fields the percentage of humus is 
greater in the first foot of soil in noninfected areas than in infected areas. 
In 20 of the fields the percentage of organic carbon in the samples from 
the first foot of soil outside the infected areas is greater than the organic 
carbon content of samples taken from the inside. In reporting studies 
of chemical changes brought about by the development of mycelium in 
fungus fairy rings, Shantz and Piemeisel (7) state that such changes 
consist largely in the reduction of organic matter by the mycelium. 
Lawes, Gilbert and Warington (5) call attention to the fact that in their 
investigations the percentage of carbon was found to be uniformly higher 
outside the ring than on the periphery or within the ring. Although the 
occurrence of less organic matter inside the majority of rootrot areas than 
outside may have no significance, the similarity of the behavior of this 
parasite to the habits of the fairy ring fungi seems to make this fact 
worth recording. No effort was made to determine if the mycelium and 
fruiting bodies played any part in the breaking down of the organic 
matter of the soil into ammonia or other compounds, but an analysis 
of the powdered fruiting bodies showed an organic nitrogen content 
of 1.73 per cent. 
EFFECT OF WEATHER CONDITIONS ON THE FORMATION OF FRUITING 
BODIES 
The production of fruiting bodies seems to be almost entirely dependent 
on weather conditions. During periods of dry, hot weather freshly 
formed conidial mats were never observed, no matter how frequently 
irrigation water was applied nor how heavy the type of soil. 
In Table III is shown the precipitation at Phoenix and Sacaton during 
the months of fruiting activity in 1917 to 1922, inclusive, and the relative 
number of fruiting bodies noted in the fields visited. It will be observed 
that the fruiting occurred in most cases during the months of heaviest 
rainfall. The apparent exception in July, 1922, was evidently influenced 
by the prolonged period of light showers and high humidity occurring 
from the 15th to the 20th. During the month of August, 1920, when 
the precipitation was 0.89 inch, the rainy periods were never as prolonged. 
Table III. —Monthly precipitation during fruiting season at Phoenix, Ariz., iQiy to IQIQ, 
and at Sacaton, Ariz., IQ20 to IQ22, and estimated number of fruiting bodies observed 
in infected fields of these localities 
1917 
1918 
1919 
1920 
1 
| 1921 
1922 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Preci¬ 
pita¬ 
tion. 
Mats 
per 
100 
square 
me¬ 
ters. 
Tune 
Inches. 
O. 1 < 
3 - 97 
0. 11 
o- 55 
Inches. 
O. 08 
I. 02 
3 * 47 
o- 39 
Inches. 
Trace 
Inches. 
O. 23 
O. 48 
O. 89 
O. 21 
Inches. 
Trace. 
Inches. 
O. II 
o -53 
3 - 3 2 
0-55 
July . 
August. . 
Sept. 
13 
8 
10 
1. 05 
2. 40 
i- 93 
19 
7 
2. 41 
3. 26 
o- 39 
1 
17 
24 
23 
42 
a 40 
a Formed the first week in September, presumably from the effect of 1.56 inches of rain August 31. This 
is the only instance noted where fruiting occurred in September. 
