198 



COMPARATIVE MORPHOLOGY OF FUNGI 



1914), the antheridium comes into open connection with the ascogonium 

 and the male nucleus migrates into the ascogonium and fuses with the 

 female (Figs. 123, 3; 126, 3). In S. mors-uvae, it goes through another 

 division before migration, so that one daughter nucleus migrates into the 



Fiq. 124. — Sphaerotheca Humuli. Development of perithecia. 1. Young antheridium 

 and ascogonium. 2. The antheridium divided into antheridial cell and stalk cell. 3. 

 Plasmogamy. 4 to 6. Development of fertilized ascogonium. ( X 500 ; after Harper, 1896.) 



ascogonium while the other remains behind in the antheridium and 

 degenerates. In a second group, as in Erysiphe Polygoni (E. Martii) on 

 Pisum sativum and Ranunculus acris, E. cichoracearum on Sonchus oler- 

 aceus, Phyllactinia corylea on Corylus Avellana, in Uncinula Salicis on 



Fig. 125. — Erysiphe Polygoni. 1. Primary ascogenous hypha with five nuclei. 2. 

 Longitudinal section through a young perithecium with three asci; the perithecial wall is 

 already differentiated. (X 470; after Harper, 1896.) 



Populus (all according to Dangeard, 1907) and in Sphaerotheca Humuli 

 var. fuliginea on Melampyrum (Winge, 1911), fertilization is absent and 

 the male nucleus degenerates in the antheridium. Thus in the 

 Erysiphaceae the relationships are apparently the same as in the Plec- 

 tascales. Although the sexual organs are normal morphologically, sexual- 



