Bacteria and Fungi 263 



destroy food. The same measures that will prevent the 

 growth of bacteria in foods will prevent the growth of the 

 molds, which are usually associated with them. 



The molds exemplify one of the fundamental characteristics 

 of the fungi ; namely, their capacity for producing enormous 

 numbers of spores. In some cases, as in the bread mold, these 

 spores are produced in rounded sacs called sporangia; in other 

 cases upright filaments of the mold develop spores by cutting 

 off chains of little rounded cells from the ends of the filaments. 

 These spores are of various colors, — brown, black, blue, green, 

 or yellow, — and they give the characteristic color to the 

 mold. In most molds the spores begin to develop at ordinary 

 temperatures within 2 or 3 days after the parent spore germi- 

 nates. 



The rusts. Among the most serious diseases affecting 

 wheat, rye, barley, and oats are those produced by the fungi 

 known as the rusts. These fungi are called rusts because 

 plants that are infected with them develop yellow and brown 

 spots that have the appearance of iron rust. The rusts occur 

 wherever grains are grown, and they cause millions of dol- 

 lars' worth of damage to crops every year. 



The rusts are parasites that live inside the host plants and 

 injure or destroy the tissues which are concerned in food manu- 

 facture. Their life history is peculiar in that the fungus usually 

 produces diseases on two different kinds of host plants. The 

 stem rust of wheat, for example, produces patches of red 

 spores which will infect other wheat plants. It produces also 

 black spores which live over winter on the stubble, and 

 which germinate the following spring and produce a third kind 

 of spore that infects the barberry. On the barberry leaves 

 the fungus produces a cuplike depression within which a fourth 



