42 Minnesota Plant Diseases. 



survive. These saprophytes are therefore of great economic 

 importance in two ways. In man's narrower economy they 

 are directly injurious in the enormous losses sustained in the 

 decay of woods and timbers. In the broader economy of 

 nature they are of inestimable value for they are the garbage- 

 destroyers which keep down the accumulation of plant debris. 

 As such their use vastly outweighs those effects detrimental to 

 man's interest. 



Bees-nest-dwelling habit and others. Certain fungi, whose 

 near relatives are the blue molds, are often found on nests of 

 bees and wasps. They have learned to utilize for their nourish- 

 ment the material of which the nest is made and so well have 

 they learned this method that they are unable to thrive on 

 any other material. One therefore finds certain fungi confined 

 to such material. Other fungi also related to the blue molds 

 are found on horn. They are able to produce a horn-destroy- 

 ing substance which makes the horn material available for the 

 fungus food. One finds such fungi on old cattle horns, or 

 horses' hoofs, and it is only on such substances that they are 

 found. Again, certain fungi occur on bones and still others 

 on feathers. One of the most common of the feather-inhabit- 

 ing fungi is also a blue mold relative. 



Fungus-dwelling habit. A very common habit among 

 fungi is that of living on other fungi. This is especially the 

 case among those molds which live on plants of the mushroom 

 group. A mushroom placed in a closed moist chamber will 

 soon be covered with mold-growths of various kinds. These 

 molds are for the most part truly saprophytic, though some are 

 capable of parasitism during a part of their life history. 



Honey-dew-dwelling habit. There is a great group oi 

 fungi which are known as "honey-dew" fungi and for the most 

 part belong to the "burnt wood" groups. They are true sapro- 

 phytes and live on the excretions and secretions deposited by 

 various insects upon the surfaces of leaves and twigs. They 

 often show an exact selection for the secretion of certain kinds 

 of insects. A fungus of spongy appearance, for instance, al- 

 ways appears on the woolly aphis secretions. After the death 

 of the insect the dead remains of the body become incorporated 

 with the secretions and the whole forms a mass in which the 



