SPHAERIALES 



271 



the inner tissue is considerably altered and crumbled, the peripheral 

 hyphae awake to new life and penetrate the crumbling interior of the 

 leaf. Earlier, when the leaf was alive, they could only penetrate between 

 epidermis and cuticle but they now penetrate the dead tissue in all 

 directions. 



Fig. 180. — Venturia inaequalis. Development of perithecia. 1, 2. Helical hyphae. 

 3. Section through primordium of peritheeium, still showing its development from helical 

 hyphae. 4. Somewhat older stage, the ascogonium already divided into several cells. 

 5. The same, the terminal cell beginning to develop as a trichogyne. 6. The antheridium 

 is surrounding the trichogyne at the right. 7. Section through a trichogyne fusing with an 

 antheridium. 8. Section of trichogyne after nuclear migration, the male nuclei already at 

 the lower end of the trichogyne. ( X 580; after Killian, 1917.) 



In this second saprophytic phase the formation of perithecia begins. 

 •Here and there a remaining hyphal branch, which is not further differ- 

 entiated from a purely vegetative hypha, coils to a helix (Fig. 180, 1); 

 at first it is aseptate, then separated into binucleate cells. The cells of 

 the helix lie close together in a plectenchymatic knot, with the peripheral 

 cell walls much thickened (Fig. 180, 2). The helical arrangement is 



