500 



SPECIAL PLANT PATHOLOGY 



temperature conditions were favorable. Ascospores were not expelled 

 during the warm winter rains, but during the summer rains ascospores 



Fig. 177. — Spore-sacs or asci with eight two-celled ascospores of chestnut blight 

 fungus (Endoihia parasitica). Below diagram showing relative size of pycnospores 

 (left) and ascospores (right). (After Heald, F. D., Bull. 5, Chestnut Tree Blight 

 Cojn., 1913.) 



are forcibly expelled in large numbers from the perithecia during and 

 after each warm rain in case the amount of rain is sufficient to soak up 



