APPENDIX 273 



the dust from a dry dust cloth over one of them. After leaving it 

 thus exposed to the air for two minutes replace the cover. Over a 

 second dish shake a damp dust cloth. Set both aside and compare 

 the number of molds that grow in the two plates. Has the dampness 

 prevented the distribution of mold spores ? 



8. Molds in the Air. Prepare four dishes of hardened gelatin. 

 Expose two of them to the air of an ordinary room that has been 

 quiet for some hours, for example a schoolroom before the school 

 has assembled, by leaving the cover off for two minutes and then 

 replacing it. Expose two other plates for the same length of time 

 at the close of the school session after the air has become stirred up. 

 Another pair of plates may be advantageously exposed in the hall 

 while the scholars are passing. All plates should be exposed for the 

 same length of time, carefully labeled, and set aside at the ordinary 

 room temperature for growth. Count the number of molds that 

 grow in each plate. A few bacteria colonies will be likely to appear 

 on some of the plates, but these can easily be distinguished from 

 molds since they do not have the fuzzy appearance due to the mold 

 mycelium. 



g. Molds in the Air. Repeat the above experiment, using moist 

 bread instead of the petri dishes of gelatin. After exposure, place 

 under bell glasses and set aside for growth. The results will be 

 essentially the same as in the last experiment, though less striking. 



10. Growth from Spores. Prepare a petri dish of hardened gela- 

 tin. With a platinum wire or the tip of a knife blade remove a bit 

 of the spore mass from some mold obtained in a previous experiment, 

 and transfer it to the surface of the gelatin. Touch the gelatin in 

 this way in several places and then cover and set aside for growth. 

 After two or three days note that a mold colony begins to grow from 

 each spot where the wire touched, indicating that spores have been 

 transferred to the jelly. Allow the molds to grow for two or three 

 days, examining them each day with a microscope or, if a microscope 

 is not at hand, with a hand lens. Note the extension of the mycelium 

 through the gelatin, and later the development of minute tufts of 

 spores on the surface. 



11. Germination of Spores. Sow mold spores upon the surface 

 of a petri dish of hardened gelatin as follows. Select one of the 



