STIMULATORY EFFECTS 143 



Pestalozzia sp., Chaetomella sp. (all from cranberry), Diplodia sp. 

 (from lime fruit), Aspergillus niger, Penicillium italicum, Col- 

 letotrichum gloeosporioides, and Ceuthospora limitata. The fol- 

 lowing species, however, were killed by this treatment: Rhizopus 

 nigricans, Penicillium digitatum, P. expansum, Phomopsis citri, 

 Glomerella rufo-maculans, Gloeosporium limetticolum, Antho- 

 stromella destruens, Ac author hynchus vaccinii, Gloeosporium 

 minus, Alelanconium sp. (from grape), Fusarium sp. (from 

 orange), Botrytis sp. (from apple), Phytophthora sp. (from 

 orange), and Guignardia sp. (from cranberry). Similar studies 

 by Landen (1939) were concerned primarily with attempts to 

 destroy the viability of chlamydospores and sporidia of Ustilago 

 zeae. Employing a large crystal-quartz monochromator, he found 

 that sporidia are more sensitive than chlamydospores. Long ul- 

 traviolet rays between 3022 and 3 130 A required a dosage of 

 1.5 X 10° ergs/mm 2 to be lethal. Dillon-Weston and Hainan 

 (1930) irradiated cultures of several species, including Rhizopus 

 nigricans, Dematium pulhdans, Neurospora sitophila, and Sclero- 

 tinia trifoliorum. They employed daily exposures with low in- 

 tensities and therewith merely modified the rate of growth. 



Germination of the urediniospores of Puccinia graminis tritici 

 was inhibited if they were floated on the surface of water during 

 exposure to sunlight, but if they were placed in the dark under 

 otherwise similar conditions, they germinated readily [Dillon- 

 Weston (1931)]. Similar results followed if he exposed them 

 to a mercury-vapor lamp for ultraviolet radiations. 



STIMULATORY EFFECTS 



The evidence on stimulation of fungi by ultraviolet light is 

 contradictory. The results of studies by a number of workers 

 indicate that exposure to such light is followed by an increased 

 growth rate. Using Fusarium eumartii, Smith (1935) found that 

 irradiated cultures were at first retarded, but that the rate of 

 growth was increased after the period of retardation. In such 

 cultures the total growth was never greater than that in the con- 

 trols. Since temperature and the accumulation of labile nutritive 

 products also favored an increased rate of growth, Smith regarded 

 stimulation as an indirect effect of radiation. This interpretation 

 is not in accord with the results of Hutchinson and Newton 



