NO. 23 STIMULATION OF ALGAE BY ULTRAVIOLET MEIER 3 



with cardboard to serve as a control. By means of various screens 

 the activating region was found to lie probably between 2760 and 

 3130 A. 



Nadson and Philippov (1928) used a quartz mercury-vapor lamp to 

 irradiate petri-dish cultures of pure cultures of yeasts and fungi 

 covered with thick glass or metal with an opening in the center. The 

 growth directly under the opening was completely destroyed by the 

 ultraviolet. The part protected by the screen developed normally, but 

 immediately surrounding the sterile zone was a bracelet of very intense 

 growth where the culture partially protected by the screen had been 

 touched by only the oblique rays. The yeasts in this region presented 

 exaggerated budding ; for example, the cell of the yeast Nadsonia 

 fulvcsccns, which normally forms from one to three buds, in this 

 case formed at its extremities whole groups or bouquets of buds. The 

 mother cell, excited by the irradiation to such intense multiplication, 

 swelled up, then, worn out, degenerated and perished. The group 

 of young cells, dissociated by this fact, continued to live inde- 

 pendently and to multiply by budding. In the zone of stimulation, 

 Mucor guilliermondii asexually produced large quantities of sporangia, 

 while on the other hand, sexual reproduction of Mucor genevensis 

 was stimulated. 



Ramsey and Bailey (1930) found a definite stimulation of spore 

 production in cultures of Macrosporium tomato and Fusarium cepae 

 on exposure to ultraviolet radiation from a quartz mercury arc. The 

 greatest amount of spore production occurred when filters with the 

 lower limits of transmission between 2535 and 2800 A. were used. 

 There was stimulation also with irradiations of 2535 A. and shorter 

 wave lengths, but with these exposures there was also some lethal 

 effect and inhibition of mycelial development. 



Hutchinson and Ashton (1930), using a quartz mercury-vapor 

 lamp and a Hilger monochromatic illuminator, found that irradiation 

 with the short wave length 2700 A. caused early retardation of growth 

 followed by stimulation in the fungus Colletotrichum phomoides and 

 in yeast. Early sporulation of Colletotrichum resulted from irradia- 

 tion with 3132, 3022, 2804, 2700, 2054, and 1854 A. ; early acervuli 

 development occurred after irradiation with 2535 A. 



Smith (1935) reports stimulated spore production in Fusarium 

 eumartii Carp., regardless of the growth rate of the fungus after ir- 

 radiation with a Cooper-Hewitt mercury arc lamp. 



De Fazi and de Fazi (1915) describe experiments showing that 

 Saccharomyces opuntiae, when irradiated with ultraviolet, lived, re- 

 produced, and fermented more actively. 



