Sept is, 1923 
Corticium vagum on the Pea and Bean 
447 
Balls points out that the sensitiveness of Corticium vagum to its own 
metabolic products would explain the decreased pathogenicity at the 
higher temperatures. Again, a decrease in pathogenic power may 
result from the definite tendency of the fungus to grow more super¬ 
ficially on the substratum at the higher temperatures, while closely 
adhering to the substratum at the lower temperatures. With respect 
to the optimum temperature for tissue destruction, it is quite probable 
that in the last analysis we are dealing with an enzym, or a group of 
enzyms, which are secreted more abundantly at i8° C., or which react 
more vigorously on the host tissue at this particular temperature. At 
present we have no direct evidence of such enzym activity of Corticium 
vagum. It is interesting in this connection, however, to note that Jones 
(8) obtained a more abundant secretion of cytolytic enzyms from Bacillus 
carotovorus at 18° to 21 0 than at the higher temperatures of from 25 0 to 28°. 
Studies of the enzymatic activities of Corticium vagum would undoubt¬ 
edly throw much light on this particular relation. 
The nature of the parasitism exhibited by Corticium vagum offers 
interesting material for speculation. In the first place, it is evident 
that in the injury and destruction of growing points of the potatoes and 
plumules of the pea and the bean, we are dealing largely with a question 
of escape. As has been suggested, the early growth of the various 
hosts in the soil above 21 0 C. is so rapid as to permit the tender bud por¬ 
tion to push through the soil with little or no injury. This was found 
especially true of the potato shoots. On the other hand, the lower tem¬ 
peratures retard the host growth and increase the exposure at just those 
temperatures which are most favorable for tissue destruction. Such 
retardation as shown is frequently disastrous. With tissue destruction 
in general, however, it appears that we are concerned with a specific 
type of parasitism determined, as stated, by a fixed character of the 
fungus and one closely allied to its saprophytic activity. What this 
fixed physiological factor, or factors, in the fungus is remains undeter¬ 
mined. Favorable soil temperature and closeness of contact, however, 
appear as important relations in this peculiar parasitism. 
It seems reasonable to suggest that, given an opportunity for closeness 
of contact, the action of the fungus in the soil upon living tissue is not 
widely different from that on nonliving organic matter. Were such 
the case, it appears possible that in the pathogenic activities of Cortir 
cium vagum we are dealing with the action of one or a group of enzyms 
whose temperature relations differ but little, regardless of whether the 
substances acted upon under natural conditions of the soil belong to 
the living or nonliving organic world. The approximate coincidence of 
the temperature range for saprophytic growth and for parasitism, the 
apparent complete lack of host specialization, the similar temperature 
range for destruction of tissue of the various hosts, together with the 
peculiar nature of the lesions produced by the fungus, and finally the 
wide range of hosts, limited in number perhaps only by our lack of 
observation—all seem to support such a view. With Corticium vagum 
it appears that we are concerned with a peculiar type of parasitism quite 
distinct from that exhibited by the more specialized parasites. The 
recent works of Ames (r), Edson and Shapovalov (7), and Shapovalov 
(16), are interesting in the suggestion that a large number of saprophytes 
may destroy living tissues tinder certain conditions especially favorable 
for their growth. 
60096—23-2 
