THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 255 



ascogonium itself and a second in the ascogenous hypha, and hence, to bring 

 the chromosome number back to the monoploid, two reduction divisions 

 are necessary. According to many workers a nuclear fusion does not occur in 

 the ascogonium, but there is merely an association of nuclei, and they consider 



Fig. 246. — Sphaerotheca hutmili. Sexual . reproduction. A, Associated 

 ascogonium and antheridium. B, Ascogonium with male and female 

 nuclei, the antheridium lies behind the ascogonium. C, Male and 

 female nuclei in ascogonium. D and E, Ascogonium with fusion 

 nucleus. F, Formation of perithecium and division of ascogonium into 

 a row of four cells, the penultimate cell of which is binucleate. (After 

 Harper.) 



that the only true fusion occurs in the ascogenous hypha. If this is the case 

 there is only one reduction division, namely the first division of the nucleus 

 in the ascus. 



During development the wall of the perithecium becomes differentiated 

 into inner and outer layers, which can be easily distinguished. The inner 

 layer is made up of thin-walled cells, rich in protoplasm. It forms a packing 

 round the developing asci and supplies them with food. The function of the 

 outer layer is for protection. Its cells have scanty contents and their walls 

 undergo a change analogous to lignification. 



From special cells of this layer the characteristic filamentous appendages 

 are differentiated. These appendages consist of long, single-celled outgrowths 



