Minnesota Plant Diseases. 



43 



fungus thrives. The mycelium of such honey-dew fungi is usu- 

 ally black in color and looks like partially burnt wood. These 

 fungi are usually true saprophytes and do not attack the living 

 leaves or plant parts on which they develop. They may, how- 

 ever, grow in such abundance on the surface of the leaves that 

 they cut out the light and hence injure the plant by prohibiting 

 the leaf in its starch-making function. The secretions of in- 

 sects, especially when the latter are abundant, are often evenly 

 distributed over leaf surfaces and hence the fungus may be- 

 come very evenly and abundantly distributed over the foliage. 



Food-mold habit. It is the common experience of every 

 housewife that bread and cake, and starchy material in general, 

 is subject to molding. Such molding is due to the presence of 

 certain fungi known as black or bread molds. They develop on 

 all kinds of starch foods and especially where these are kept 

 moist, as often happens in improperly ventilated bread boxes. 

 Such fungi will commonly grow in sugar solutions. The molds 

 of preserves are also common enemies of the housewife. These 

 are for the most part fungi of the blue or green mold group. 

 When fruit is preserved in jars spores of such molds are intro- 

 duced with the fruit and those near the lid have access to the 

 included air or to air which leaks in through imperfectly fitting 

 covers. These spores develop into the blue or green mold 

 plants and produce the scum which is so often found under the 

 jar covers. When paraffin is poured on preserves it forms a 

 close-fitting, air-tight cover and does not allow any molds to 

 develop. It is well known how cheese when allowed to remain 

 under moist conditions for any length of time will produce, 

 especially on the rind surface, green patches of mold which, 

 unless removed, increase in size until they cover the whole 

 cheese. This mold is a saprophytic fungus and the green color 

 is due to the millions of spores produced on much-branched 

 threads. Green molds are purposely cultivated in certain kinds 

 of cheese to which they impart peculiar flavors. 



"Mildew" of clothes. When moist clothes are left in closed, 

 badly ventilated receptacles for any length of time they "mil- 

 dew" or get moldy. This condition is due to the growth of 

 fungi which feed on the cotton or wool fibers. It is only under 

 moist and undisturbed conditions that such will grow. An air- 



