Feb. 3. 1919 Physoderma Disease of Corn 149 



from a field trip four weeks later, June 14, he found that the disease had 

 developed to a more or less extent on most of the plants which were inoc- 

 ulated (PI. 12). 



In cases where infections were obtained, the upper leaves, which were 

 in the bud at the time of inoculation, showed the disease near their tips, 

 while leaves which were mature were diseased at the base. This explains 

 in part the fact that in the field the disease may be present only on the 

 tips of blades or confined to the basal parts. The occurrence of the dis- 

 ease in bands of alternating heavy and light infection across the blades, 

 which is often very noticeable, is no doubt due to the effect on sporangia 

 germination of alternating periods of favorable and unfavorable tem- 

 perature and moisture conditions while the leaves are emerging from the 

 bud. The part of the blade which happened to be in contact with the 

 bud water while the zoospores were being liberated became infected. 



OVERWINTERING OF THE SPORANGIA 



The sporangia of Physoderma zeae-maydis pass the winter in the old 

 infected plants and in the soil, and germinate the following summer to 

 produce new infections. Through the kindness of Dr. H. E. Stevens, of 

 the Florida Agricultural College, fresh sporangial material was obtained 

 from Florida at four- week intervals from January to April, 191 7. These 

 sporangia were found to be viable each time. Sporangia collected at the 

 Alabama and Mississippi stations in May and June of the same year 

 germinated readily. Sporangia buried about 3 inches deep at Clemson 

 College, S. C, September 7, 191 7, germinated in small percentages as 

 late as July 20, 191 8. These sporangia were taken from the soil on 

 July 10. Sporangia left aboveground at the same point germinated also. 

 Sporangia taken from the field on January 5 at Agricultural College, 

 Miss., and buried 3 to 5 inches deep germinated about 50 per cent on 

 June 20. Sporangia which remained aboveground in an open box gave 

 a lower percentage of germination. This may be due to the fact that 

 the sporangia aboveground were much drier when the tests were made. 

 The winter was severe at this point, the temperature at one time being 

 as low as zero Fahrenheit. This temperature apparently does not 

 injure the sporangia, as the author had allowed sporangia to freeze in a 

 cake of ice at the Wisconsin Station when the temperature was —8° F. 

 After several days the ice was melted from the sporangia, and some of 

 them germinated. Sporangia collected in Alabama, Florida, and Missis- 

 sippi in June, 1918, showed a high percentage of viability. Sporangia 

 collected in South Carolina as late as July were found to be viable. 

 Later tests than these have not been made, and it may be possible that 

 these sporangia live in the old infected plants and in the soil for a number 

 of years. Material has been prepared for further tests. 



