Sept, is, 1933 
Corticium vagum on the Pea and Bean 
445 
The ratio at which the fungus growth increased with rise in the tem¬ 
perature is an especially interesting phase of the studies. Balls (3) 
found that the growth rate of the specific strain of the Rhizoctonia stage 
of Corticium vagum with which he worked accorded for a very short 
period with Van’t Hoff’s law. This same growth relation has been found 
true within certain limits for the pea by Leitch (jo) and for the com by 
Lehenbauer (9). In these studies a constant coefficient for each incre¬ 
ment of io° C. rise in temperature was not found; on the other hand, as 
shown in Table IX, a progressive decreasing coefficient resulted with 
increase in temperature. Owing in part to the operation of the possible 
“time factor” during the 96 hours of exposure, the specific value which 
might be predicted from the Van’t Hoff law was approximated only 
within the narrow range between 14 0 and 25 0 C. What relation the 
progressively decreasing coefficient might have to the pathogenicity of 
the fungus is not clear, although it would appear significant in view of 
Balls’s conclusions that “some (deleterious) products are formed at the 
low as at the high temperatures but at a much slower rate.” Were such 
varying quantities of by-products present in the mycelium at the different 
temperatures as suggested, it would appear that they might be important 
in determining the varying degrees of closeness to which the hyphae of 
Corticium vagum grew to the substratum throughout the temperature 
range for fungal growth, a relation described in the following paragraph. 
As closeness of contact is of undoubted importance in the pathogenicity 
of the fungus, the decreasing ratio value might also have special signifi¬ 
cance as a factor in its pathogenic relation and be definitely indicative of 
greater parasitic possibilities on the part of the fungus at the lower tem¬ 
peratures where, owing to slow accumulation or absence of poisonous 
products, the hyphae adhere, and even embed themselves, in the 
substratum. 
In addition to the fact that the hyphae grew exclusively from an apical 
zone, Balls (3) determined that the mycelia exhibited different growth 
characteristics at various temperatures. In liquid media at 20° C. he 
found that the hyphae grew straight and became slightly branched. At 
34 0 in liquid media a fluffy mycelial growth resulted; more numerous 
short hyphae and fewer resting cells developed than at 20°. A num¬ 
ber of these features were especially evident in the present study. At 
the lower temperatures the hyphae became sparsely branched and grew 
widely separated in the colony. The most characteristic feature lay in 
the fact that the hyphae at temperatures below 15 0 grew closely in 
contact with the medium (agar), and at still lower temperatures, as stated, 
definitely embedded themselves in it. Mycelia so developed appeared 
hyalin in color, and for considerable periods would remain almost indis¬ 
tinguishable from the media. Normal pigmentation and resting-cell 
formation were found to be greatly delayed at these lower temperatures 
as compared with the higher temperatures. With higher temperatures 
the mycelia branched more profusely and produced a more superficial 
type of growth upon the substratum. Between 24 0 and 28° profuse 
mycelial growth resulted frequently with definite aerial hyphae, often 
growing in a direction at right angles to the substratum. The character¬ 
istic brown pigment, together with the resting cells and consequent 
sclerotia formation, appeared at its maximum within this particular tem¬ 
perature range. These latter characteristics were found to decrease with 
increase of temperature above 27 0 and 28°, resulting in smaller colonies 
consisting of fluffy, aerial, short, but frequently branched, hyphae. 
