APPENDIX 299 



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 distribu- 

 tion of mold spores ? 



8. Molds in the Air (a). Prepare four dishes of hardened agar. 

 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. 



9. Holds in the Air (6). Repeat the above experiment, using moist 

 bread instead of the petri dishes of agar. 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 agar. 

 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 agar. Touch the agar 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 trans- 

 ferred 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 myceUum 

 through the agar, 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 agar as follows : Select one of the 



