LIFE HISTORIES OF FUNGI 269 



261. Reproduction by Asci. In late summer or early 

 fall one may notice, on an infected leaf, among the my- 

 celium, tiny black dots or spheres (Fig. 194), whence the 

 name, Microsphcera. Examined with the microscope, these 

 bodies are seen to bear numerous appendages, branched 

 at the end, and with the tips of the branches curved back to 

 form miniature hooks (Fig. 195). When these little spheres 

 are crushed, or when they burst open, they are found to con- 



FIG. 194. Powdery mildew (Microsphcera Alni] on lilac leaf. An in- 

 fected area from the leaf in Fig. 193, greatly magnified. 



tain a number of tiny sacs or asci (singular ascus), whence 

 the name "sac-fungus," or Ascomycete. In each ascus are 

 a number of spores or ascospores, formed from the con- 

 tents of the ascus. The young ascus is, therefore, a spore- 

 mother-cell. There are usually eight ascospores in an 

 ascus, but the number may vary. 



The spherical case containing the asci is the "spore- 

 fruit" (ascocarp or perithecium), and results from the 

 fusion of the contents of an antheridium and an oogonium 



