42 



BACTERIA, YEASTS, AND MOLDS 



to find their way to the skin of any piece of fruit. But 

 after they fall upon the fruit they will not grow unless 

 the conditions are right. If the skin is whole and smooth 

 and dry, they do not readily germinate. Commonly they 

 start at some small crack in the skin through which the 

 thread sprouting from the spore can thrust itself into 



the softer parts within. 

 Hence whole-skinned fruits 

 are easier to keep than those 

 with bruises. If the spores 

 find sufficient moisture on the 

 skin, and a convenient crack, 

 they soon send a tiny myce- 

 lium thread into the fruit. 

 This grows luxuriantly, 

 branching profusely, and 

 presently pushes its way in 

 every direction through the 

 soft pulp of the fruit. The 

 fruit begins to soften and 

 decay. The rotting is caused 

 by the growth of the mold 

 mycelium in the flesh, the 

 visible decaying spots being 

 simply the external evidence of the mold growing within. 

 After a time the mold begins to form its spores. To 

 do this it generally breaks through the skin so that the 

 spores may be formed in the air. These spores can easily 

 be seen in a well-decayed apple (Fig. 25). The spores 

 thus produced are then scattered into the air from the 

 broken skin of the fruit. They are carried either by air 



Fig. 23. Monilia, showing the for- 

 mation of spores at c and the 

 sprouting of spores at a and b. 



