Abstract
The possibility of producing mutations by ultraviolet rays is still under discussion. Since the indecisive results of Guyenot 1 on Drosophila ampelophila, experiments have been undertaken, amongst others, by Altenburg 2 on Drosophila melanogaster, by MacDougall 3 on Chilodon uncinatus, and by Stubbe 4 on Antirrhinum majus. While the attempts of Altenburg gave completely negative results, MacDougall described several new hereditary forms of Chilodon produced by ultraviolet radiation and Stubbe found a percentage of mutants almost as high with ultraviolet as obtained with X-rays, 85.71 and 87.012 respectively.
Since the spores and mycelia of the Mucoraceae are sensitive to a small quantity of ultraviolet radiation and present a relatively simple unicellular structure they seem particularly promising for the study of the present problem.
Ten generations of Rhizopus nigricans were irradiated for periods of time a little less than sufficient to kill them.
The fungus was cultivated on agarized Coon's medium in Petri dishes uncovered during exposures. The spores collected from the culture of one generation by means of a soft wet brush were spread on the surface of the medium used for the following generation. The latter was irradiated either immediately after the absorption of the water brought in by the brush or after 15 hours, the mycelia having developed. (22°C.)
I used the total radiations of an arc mercury lamp, working with 4 amperes and 60 volts on direct current. The distance between the lamp and the culture was 30 cm. The time of exposure for the spores was 35 seconds and 20 for the mycelia. (Lethal doses were 25 and 15 seconds, respectively.) 5
A careful examination of the morphological and physiological behavior of the 10 irradiated generations did not show the least difference between them and the control cultures.
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