Von. XXV Washington, D. C., September 15, 1923 No. 11 
SOIL TEMPERATURE AS A FACTOR AFFECTING THE 
PATHOGENICITY OF CORTICIUM VAGUM ON THE PEA 
AND THE BEAN 1 
By B. b- Richards 
Department of Botany and Plant Pathology, Utah Agricultural Experiment Station 
INTRODUCTION 
The present paper is the third of a series of articles 2 dealing with the 
> effects of soil temperature on the pathogenicity of Corticium vagum 
B. and C. The two earlier publications (13, 14 ) 3 dealt primarily with 
the power of this organism to produce cankers on the stems of the Irish 
potato. In these publications results were presented from both field 
and greenhouse experiments which showed a definite and vital relation 
to exist between the temperature of the soil and the pathogenic action of 
Corticium vagum on this particular host. Such opportunity for further 
study of the parasitism of this organism was offered by the wide range of 
hosts on which the sterile or “ Rhizoctonia” stage of Corticium vagum 
becomes parasitic, that studies similar to those on the potato were ex- 
tended to include a number of additional hosts. The results of such 
studies on the pea and the bean, together with observations on the growth 
, reaction of the fungus to temperature^ are included in the following 
article. 
APPARATUS AND METHODS 
In the various pathogenicity studies the host plants w;ere grpwn in 
metal cans 7 inches in diameter and 12 inpties deep. These were sub¬ 
merged in a series of water jackets known at the .University of Wisconsin 
as the Wisconsin soil-temperature tanks. { These tanks, together yrith the 
methods for temperature and.soil-moisture control,,.were <^crifce<^ i# the 
earlier work, on the potato (15). Such variations in the methods. } aud 
operations as were therein employed will receive consideration m relation 
to the individual experiments. 
Temperatures given in the various tables ^represent the mean tempera¬ 
tures at which the water was maintained in each of thp different Tanks. 
Fluctuations in these temperatures did not. exceed in gpnpr^J more Than 
one and one-half degrees from those giyen in the tables, evep.aS the 
extreme high and low temperatures, a^d were nof ; of ,tppv§ a .few 
hours' duration. Although the surface soil in the pans was kept ap¬ 
proximately 2 inches below the surface of the water uji the tanks, the soil 
1 Accepted for publkationjune 25, 1923. 
* The series of three articles on the “ Pathogenicity of Corticium vagum ” was presented to the faculty of 
th'e Uhiv^ity df W^cbhsMin partialfulfillment Of the requirements for the degre§ of Doctor of Philosophy. 
, The ;vmter Tfishcis to &tpfess his indebtedness to Prof ;X. Rv Jones for helpful criticism'and suggestions. 
* Reference ismadeby number (italics) to “Iyiterature cited”, p. 449- 
Journal of Agricultural Research, 
Washington, D. C. 
*gi 
(431) 
Vol. XXV, No. n 
Sept. 15/1923 € 
Key No. Utah—18 
60096—23-1 
