CHESTNUT DISEASES 



145 



grow out from the point of infection in all directions, the tissues 

 of the bark are killed and soon a rapidly enlarging canker be- 

 comes apparent. 



About a month after infection is accomplished, the surface 

 of the small canker becomes covered with numerous small 

 blisters (Fig. 19). These blisters are produced by balls of 

 mycelium formed under the cork-layer. Within these balls 

 are formed one of the types of spores (the conidia). During 

 moist conditions, following rains, 

 long, twisted, yellow tendrils are 

 pushed out from the ruptured bark 

 over each blister (Fig. 19). The 

 tendrils are a mass of the very 

 small spores dried into this shape 

 after being squeezed through a 

 small opening. The next rain or 

 dew causes these tendrils to sepa- 

 rate into the thousands of spores 

 in each and they then may be 

 washed or spattered about by the 

 water or carried by animate agents. 

 Any one of these spores germinat- 

 ing where the germ-tube may enter 

 wounded bark-tissue may initiate 

 a new canker. 



On older and larger cankers, the blisters and yellow tendrils 

 of spores are confined to the margin, while nearer the center, 

 reddish brown pustules of mycelium are pushed out through 

 the bark. They measure when fully developed one-sixteenth 

 of an inch or more in diameter and have numerous papillae on 

 the upper surface, each with a black dot in the tip (Fig. 20). 

 Within the brown pustules, buried below the surface of the 

 bark, are formed thirty or more cavities (perithecia), within 

 each of which are produced in great abundance another type 



Fig. 19. — Spore-horns of chest- 

 nut canker fungus. 



