Minnesota Plant Diseases. 29 



spreading the disease. The early spring spores of rusts are 

 often accompanied by structures exuding sweet fluids that are 

 attractive to insects and may be materially beneficial in the sow- 

 ing of spores. There is a certain group of fungi, often known as 

 the honey-dew fiingi, which grow chiefly on the leaves of 

 higher plants. They are not parasites but hve on insect secre- 

 tions and excreta which are deposited upon the leaves of 

 plants. In this rich pabulum the fungi grow luxuriantly and 

 often form very black sooty coats on the leaves. Such fungi 

 are often specialized to the secretions of certain specific insect 

 forms. A very curious device has been developed among the 

 so-called birds-nests fungi — a device which has to do with the 

 utilization of insects for the spreading of spores. The fruiting 



Fig. 12. — A carrion fungus. The black head at the top of the fruiting body (lying on 

 the leaf) is covered with a sticky solution in which spores are found. Insects, at- 

 tracted by the odor, carry off this solution and thus scatter the spores. Original. 



body is beaker-shaped and in the little beaker are tiny flattened 

 egg-like bodies, in reality closed cases, the interior of which 

 contains numerous spores. The "eggs-stalks" become gelat- 

 inous and very elastic when wetted and can be pulled out to a 

 comparatively enormous length. These stalks probably serve 

 to attach the "eggs" to insects' legs and later, becoming en- 

 tangled in twigs or leaves, fasten the "eggs" to these objects. 

 Germination of the spores follows immediately under favorable 

 conditions. 



Undoubted and remarkable examples of insect aid to spore 

 sowing occurs in the so-called carrion fungi. Here the spores 

 are found in a sticky, usually brownish mass, which is at matu- 



