24 



ISOLATION AND CULTIVATION OF FUNGI 



B 



filter paper is then placed lightly in the bottom part, and on it 

 are sprinkled small amounts of well-macerated tissues contain- 

 ing oospores. Blocks of 2% agar on which spore powder is 

 sprinkled can be substituted for moist filter paper. Using this 



procedure, Hiura was able to 

 study phenomena of infection, 

 as circumscribed by tempera- 

 ture and moisture [Hiura 

 (1935)]. 



In the artificial cultivation 

 of various fungi of the downy 

 and powdery mildews and the 

 rusts it is necessary to trans- 

 fer them from living plants to 

 living plants growing in a 

 more or less controlled en- 

 vironment. Determination of 

 heteroeciousness in rusts is for 

 the most part accomplished by 

 such techniques. Clinton and 

 McCormick (1924), however, 

 floated green leaves on w^ater 

 in Petri dishes and by this pro- 

 cedure successfully accom- 

 plished infection by 28 species 

 of rusts from 12 genera. 



Experiences w^ith Perono- 

 spora tabacina indicate that it 

 can be maintained in culture 

 on living tobacco plants, pro- 

 vided the inoculated plants 

 are maintained in an artificial 

 environment in which the temperature does not exceed 65° F, 

 the relative humidity is at the point of saturation, and the light 

 is diffuse. Under such conditions crops of sporangia have been 

 produced during every month of the year. Presumably other 

 downy mildews would behave similarly in a suitable artificial 

 environment. 



Maintenance of cultures. Much can be learned about a 

 given fungus if it is maintained in pure culture on a chosen 



mm 



:i i ! ii ! i i i ii i ii i iiiii i iiiii i iii i f 



1 



Fig. 7. Schematic arrangement to 

 show method for isolating Ascomy- 

 cetes that forcibly expel their asco- 

 spores. A. Poured agar plates, sur- 

 face view, over infested leaf that 

 rests upon pad of moist filter paper; 

 B, side view. The tissues in which 

 the ascocarps are embedded are ele- 

 vated on the pad to permit the 

 spores, when discharged, to reach the 

 agar surface above them. 



