Feb. 3. 1919 Physoderma Disease of Corn 141 



infection. The latter, however, might have been influenced by tempera- 

 tures. Early corn at the Pee Dee Station at Florence, S. C, was dwarfed 

 by dry weather in 191 8 and was not attacked to any great extent by the 

 fungus. At Clemson College, S. C, very early and very late com sus- 

 tained considerable injury in 191 7, while com of intermediate ages 

 suffered much less damage. The midsummer was very dry at this 

 station, while the early and late seasons were rather wet. 



(4) Apparently the more vigorous plants in certain cases sustain the 

 severest attacks. These plants, however, will not continue to look vig- 

 orous after the disease has had time to develop. The fact that these 

 vigorous plants are capable of shielding the free water which is held 

 behind the sheath and around the growing point, or bud, from the drying 

 effects of the wind and sun offers more favorable conditions for spore 

 germination and no doubt accounts for the greater percentage of infec- 

 tion on plants of this type. In low, wet fields small plants are injured 

 the same as large ones. This greater injury to large, vigorous plants 

 was more noticeable in dry territory. 



(5) Where seasons were wet — for instance, in the sections where 

 greater damage was done in 191 7 — there was httle noticeable difference 

 in the amount of infection on corn growing on high and on low lands. 

 At the South Carolina Station the most severe injury was caused to very 

 early com grown on comparatively high land. As previously men- 

 tioned, the early season was fairly wet at this point. 



(6) The disease was found on the Blue Ridge Mountains of North 

 Carolina at an elevation of about 3,000 feet, where it is claimed that 

 the summer nights are always cool. In 191 7, corn foliage was killed 

 by frost on September 1 1 at this point. Very little of the disease was 

 found at this elevation, however, even on wet lands. The disease is 

 probably held in check to a certain extent by low temperatures which 

 prevail at that elevation. A similar explanation was offered by the 

 writer, in a summary of the survey work which was given by Lyman (4, 5), 

 for the absence of serious injury by the disease in the Northern States. 

 It was also thought probable at that time that the disease had reached 

 its northern limits. This supposition was drawn from the results of 

 temperature studies of the germination of sporangia in the laboratory. 

 Since that time, however, further investigation has shown that the 

 sporangia of the fungus will germinate at a considerably lower tempera- 

 ture than was then supposed. However, the minimum temperature at 

 which they are known to germinate is rather high (23° C.) as will be 

 explained later, and it is probable that this temperature does not occur 

 commonly during and immediately after the cold rains of early summer 

 in the north. So far as is known at present, it would require a tempera- 

 ture not lower than 23° C, continuously for three days, with sufficient 

 surface water for germination, in order for severe attacks to develop 

 provided the sporangia are present on the plants. There is a question 



