THALLOPHYTA: FUNGI 



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nuclei of the ascogonium pass into the ascogenous hyphae, where they 

 multiply. The members of each pair remain together as walls are 

 formed. The terminal cell of a branch that is to become an ascus bends 

 back to form a hook and its two nuclei divide simultaneously. Three 



Fig. 106. Origin of the ascus in Pyronema confluens. A, hook formation at tip of ascog- 

 enous hypha; B, simultaneous division of nuclei; C, formation of uninucleate terminal and 

 basal cells and of binvicleate penultimate cell; D, fusion of nuclei in penultimate cell to form 

 an ascus; also migration of nucleus of basal cell into terminal cell; E, same stage except that 

 nucleus of terminal cell has migrated into basal cell; F, later stage showing development of 

 hook from basal cell; G, development of three hooks and an ascus from binucleate tip 

 of an ascogenous hypha. (After Claussen.) 



cells are now cut off by walls. The terminal and basal cells are uninu- 

 cleate but the middle one (the penultimate cell) has two nuclei of opposite 

 sex, these being the descendants of a male and female nucleus that came 

 from the fertilized ascogonium. The two nuclei may now fuse and the 

 middle cell become an ascus, or the nucleus from the terminal cell may 

 migrate into the basal cell and another hook may be formed. This 



