220 



FUNGOUS DISEASES OF PLANTS 



these layers into all available space, smaller hyphae are protruded ; 

 thus a compact inclosing body or perithecium is developed. With 

 the further growth of the perithecium and the increase in size 

 of the ascus, the inner layer and all internal hyphal branches 

 are dissolved and appropriated. Meanwhile, the outer layer be- 

 comes yellow or brown and forms the true wall of the peri- 

 thecium. From the wall cells of the perithecium there are 



Fig. 86. Spore Forms and Appendages of Erysiphace^e 



a, Erysiphe Polygoni ; &, Podosphcera Oxyacanthce ; c, Microsphara Alni ; e, Phyllactinia 

 Corylea ; d and /, Uncinula necator 



produced, either from the base or from a more or less equatorial 

 plane, the characteristic appendages. In a few cases only are 

 appendages produced from the apex. At maturity there are one 

 or more asci, depending upon the genus, and each ascus con- 

 tains normally from two to eight spores, the shape -of the ascus 

 varying from practically spherical in the one-ascus forms to 

 clavate or cylindrical where there are two or many asci. The 

 spores are one celled and colorless. As a rule the ascospores 

 do not germinate immediately, requiring a period of rest. By 



