DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 499 



4.5 to 8.6/i in size (Fig. 177). The walls are thicker than those of the 

 pycnospores. Expulsion of the ascospores is dependent upon tempera- 



-^f 





■•^'^^:!d^>^ 



Fig. 176. — A, Vertical section of a pycnidial pustule. The filaments lining the 

 cavity produce the spores that ooze out as "spore-horns;" B, vertical section of a 

 perithecial pustule. ' Several of the perithecia are cut so as to show the fuUlengths 

 of the necks in the chestnut blight fungus (Endoihia parasitica). (After Heald, 

 F. D., Bull. 5, Chestnut Tree Blight Com., 1913.) 



ture, as well as moisture. There was no expulsion of ascospores under 

 field conditions from late November until the rain of March 21, when 



