300 BACTERIA, YEASTS, AND MOLDS 



dishes previously inoculated and showing mold colonies in vigorous 

 growth, some of which bear spores. Remove the cover, invert it 

 over a second dish of hardened agar, and gently tap the dish con- 

 taining the molds. This will cause the spores to fall in a shower into 

 the second dish. Replace the cover and set the newly inoculated 

 dish aside for growth. After one day examine the surface with a 

 microscope to see if the spores have begun to germinate. Usually 

 they will not show much growth before two days. When they begin 

 to germinate study carefully with a microscope. This may be best 

 done by dropping a thin cover glass upon the surface of the agar 

 and then studying the spores with a high-power objective (^-inch). 

 The germinating spores will show threads protruding from them, as 

 shown in Fig. 4, p. 15. Examine daily for several days. After about 

 three days it will be possible to see the fruiting branches beginning 

 to grow from the ordinary threads, as shown in Fig. 5, p. 15. This 

 study is very instructive, but cannot of course be made without a 

 good microscope. 



12. Fruiting of Molds. In the same way study a variety of molds. 

 To obtain a variety is usually easy. One needs only to expose to the 

 ordinary air two or three of the petri dishes and several species of 

 mold spores are almost sure to drop in. They cannot be distinguished 

 until they begin to develop their fruit, when they can readily be sep- 

 arated by a low-power microscope or a hand lens. If the spores 

 are sown on agar, as above described, the method of development 

 of the fruit may be studied. Methods of producing fruit in the com- 

 mon molds are shown in Figs. lo-i 7. The study of two or three species 

 is sufficient, although the larger the number of studies the better. 



13. The Effect of Drying. Place under a bell glass two slices of 

 bread, one of which is damp, either naturally or by being slightly 

 moistened with water, and the other dried. Leave for two or three 

 days and notice the effect of drying in preventing the growth of 

 molds. If one slice remains dry, no molds will grow upon it though 

 the other soon becomes covered. 



14. The Effect of Boiling Temperature. In each of two test tubes 

 of agar place a small quantity of mold spores. Melt the agar in 

 the tubes at as low a heat as will melt it. Pour the contents of one 

 tube into a petri dish and cover at once. Place the other tube in 



