42 



BACTERIA, YEASTS, AND MOLDS 



Germination of Spores. The function of these spores 

 is to reproduce the plant. If one of them lights upon a 

 proper material having sufficient warmth, moisture, and 

 nourishment for its life, it soon germinates and sends out 

 from itself a little thread (Fig. $, a). This thread feeds 

 upon the material on which it is growing, and continues to 



extend and branch until within 

 a few hours a new mycelium is 

 produced, thrusting its way into 



iSpores 



^'"Spores 



Figs. i6 and 17. Two species of molds, Monilia, common in cheese. 



the food substance and developing into a typical mold. 

 After a day or two the spores are again produced (Fig. 5), 

 and the process is repeated. The air is almost always so 

 well filled with spores of molds that it is quite inipossible 

 to leave any food product exposed for any length of time 

 without a number of these living spores fjalliiig upon it. 

 If a piece of moist bread, for example, is exposed to the 

 air for a few moments in an ordinary room, and is then cov- 

 ered with a bell glass in such a way as to keep it moist, it 

 will, in the course of a day or two, become covered with 

 molds which have come from the sprouting of spores that 



