272 COMPARATIVE MORPHOLOGY OF FUNGI 



gradually lost. The uninucleate thick-walled peripheral cells of the knot 

 elongate and serve as the future one-layered peridial wall, while the thin- 

 walled inner cells still remain isodiametric and multinucleate. One of 

 the latter grows gradually to a large vermiform cell. It begins to divide 



Fig. 181. — Venturia inaequalis. Diagrammatic section of fertilized ascogonium. The 

 septa have dissolved, the nuclei are migrating to the inner cells. (X 875; after Killian, 

 1917.) 



and produces a (at most a 7-membered) chain of more or less isodia- 

 metric, bi- to quadri-nucleate cells, the future ascogonium (Fig. 180, 4). 

 The peripheral terminal cell of the ascogonium swells clavately, later 

 elongates and forms the future trichogyne (Fig. 180, 5). 



