Minnesota Plant Life. 83 



ing upon its head an elkhorn-like protuberance three or four 

 inches long. A remarkable variety of caterpillar-fungus has a 

 slender tongue of sterile tissue projected beyond the end of the 

 fruit-body area. 



Leaf-spot-fungi. Among the black fungi a considerable 

 number form what are known as leaf-spots. Very often on 

 leaves little pale areas develop, not infrequently surrounded by 

 a reddish circle. This red circle is caused by a secretion of red 

 coloring matter by the leaf, owing to the irritation occasioned 



FIG. 29. I^eaf-spot fungus growing on pear leaves. After Duggar. Bull. 145, Cornell Ag. 



Kxpt. Station. 



by the spot fungus. The pale centre of the red circle is the in- 

 jured portion of the leaf, where the fungus has destroyed the 

 cells and devoured the particles of leaf-green. If in autumn one 

 looks very closely at a leaf-spot he will generally be able to see 

 the tiny black fruit-bodies of the fungus. Usually they are 

 separate from each other as in the blight, but a considerable 

 proportion of them are blended together in layers, as was de- 

 scribed for the much larger fungus, parasitic on the toadstool. 



