SOIL FUNGI 245 



fungi, like Pen. expansum, once growth has started at ordinary tempera- 

 tures, the mycelium will continue to develop at 0°. Oxygen pressure 

 has little effect upon the germination and growth of various fungi. 

 Increased carbon dioxide pressure has a retarding effect, espe- 

 cially at low temperatures. 44 Heat has a destructive effect upon 

 fungi; the spores of Botnjtis cinerea are destroyed in ten minutes at 

 50.3° ; 45 the spores are, however, rather resistant to the action of sun- 

 light. 46 Heating for thirty minutes at 62.8°C. is sufficient to destroy 

 the conidia of most fungi, except certain species of Aspergillus. 47 The 

 morphology of the fungi is appreciably affected by the composition 

 of the medium. The nature of the mycelium, the rapidity of spore 

 formation and the color of the culture will often depend, to a greater 

 or less extent, upon the different constituents of the medium, its 

 concentration, and the environmental conditions, such as temperature 

 or aeration. For this reason, synthetic media and standard conditions 

 should be used in the study of the morphology and classification of such 

 fungi as will thrive upon them. (The same is true, of course, of other 

 microorganisms as well.) 



Isolation of single spore cultures. In the study of fungi, especially 

 their physiology, pure cultures from a single spore are prerequisites 

 for any investigation. This was pointed out by Hagem and others. 

 Some spore material is transferred by means of a platinum needle, to 

 a flask containing about 30 cc. of sterile water. After vigorous shaking 

 to separate the spores, a few cubic centimeters of the suspension is 

 poured into a second flask containing sterile water. This is repeated 

 once more, and 2 cc. of the final dilution is poured into a Petri dish con- 

 taining solid nutrient material, moistening the whole surface of the 

 plate; the excess water is then poured off. The plates are allowed 

 to incubate for 2 to 3 days and are examined under the microscope 

 for isolated growth derived from a single spore. This examination 

 can be carried out by removing the cover from the Petri dish; also by 



44 Kostytschew, S., and Afanassiewa, M. Die Verarbeitung verschiedener 

 organischer Verbindungen durch Schimmelpilze bei Sauerstoffmangel. Jahrb. 

 Wiss. Bot., 60: 628-650. 1921. 



45 Smith, J. H. The killing of Botrytis cinerea by heat, with a note on the 

 determination of temperature coefficients. Ann. Appl. Biol., 10: 335-347. 1923. 



46 Weinzirl, J. The resistance of mold spores to the action of sunlight. Univ. 

 Wis. Studies in Science. 1921, No. 2, 55-59. 



47 Thorn, C. T., and Ayers, S. H. Effect of pasteuriza.tiQU on mold spores. 

 Jour. Agr. Res., 6: 153-166. 1916. 



