PERISPORIALES 



199 



ity is degenerating; in some species the sexual act still occurs, in others 

 it is absent and the ascogonia develop parthenogenetically; in still others, 

 as in Sphaerotheca Humuli, the behavior varies according to circumstances 



Fig. 126. — Phyllactinia corylea. 1. Coiled copulation branches. The male nucleus 

 has divided to form a stalk cell and antheridial cell. 2. Antheridium completely divided 

 into stalk cell and antheridial cell. 3. Plasmogamy. 4. Caryogamy. 5. Outgrowth of 

 primary ascogenous hyphae. 6, 7. The binucleate penultimate cell of the primary ascogen- 

 ous hypha (the ultimate cell is in the next section). 8, 9. The penultimate cell develops 

 secondary ascogenous hyphae. (These figures represent successive, serial sections of the 

 same hypha.) 10, 11. Young fructifications, the former .showing ascogenous hyphae, the 

 second young asci. (1 to 4, 8, 9 X 670; 5, 6 X 250; 4, 7, 10 X 330; 11 X 200; after Harper, 

 1905.) 



and the ascogonia may continue their development with or without 

 fertilization. 



According to the type of the further development, the fertilized or the 

 unfertilized ascogonium grows while the antheridium collapses to a 



