Ill] 



ERYSIPHALES 



87 



lose their contents and are displaced by the developing asci. Later the 

 fusion of the two nuclei in each ascus takes place, and in each eight spores 

 are formed. 



Dangeard, investigating the development of E. Polygoni and E. Cicho- 

 racearum, notes that in his material the oogonium underwent septation 

 before a row of nuclei was formed, and that cells other than the penultimate 

 contained two or more nuclei. Usually in E. Cichoracearum and sometimes 

 in E. Polygoni the oogonial branch consisted of two cells; this corresponds 

 with the arrangement in the antheridial branch, which is regularly bicellular. 

 In both cases the lower cell is to be regarded as a stalk. In regard to the 

 occurrence of fertilization Dangeard's conclusions correspond with those 

 which he reached in relation to Sphaerotheca. 



Phyllactinia Corylea infects the leaves of deciduous trees and shrubs in- 

 cluding ash, oak, beech, hazel and hornbeam. 



The sexual organs arise (Harper 1905), as in other mildews, where two 

 hyphae intersect. They become closely applied to each other, and, as the 

 oogonium grows more quickly than the antheridial branch, it becomes some- 

 what twisted around the latter. The subsequent history is very like that of 

 Sphaerotheca or Erysiphe. A uninucleate antheridium is cut off, the male 

 nucleus enters the female organ (fig. 44a), nuclear fusion takes place, the 



Fig. 44. Phyllactinia Corylea (Pers.) Karst. ; a. fertilization; 

 b. fusion nucleus in oogonium ; c. d. young perithecia ; after 

 Harper. 



oogonium elongates and enlarges in diameter and the fusion nucleus divides. 

 The first nuclear division is apparently never accompanied by cell wall 

 formation, so that a binucleate stage persists for some time. Finally, however, 



