252 A TEXTBOOK OF THEORETICAL BOTANY 



up around them and the whole structure becomes enclosed in a two-layered 

 envelope, the perithecium, the inner layer of which forms a nutritive tissue, 

 while the outer serves for protection. This latter tissue secretes a bright 

 yellow substance which makes the sexual reproductive bodies easily 

 recognizable. 



After the fusion of nuclei within the ascus the zygote nucleus so formed 

 divides meiotically into four, and this is followed by a further mitotic 



Ascogenous Hypha 



Male Gamete 



Asco 



dium 



Aspergillus Pla 

 Fig. 243. — Life-cycle of Aspergillus herhariorum. 



division. Around each of these eight nuclei a wall is laid down forming an 



ascospore. These spores have a sculptured 

 epispore wall and are rounded in shape. 

 They are liberated upon the decay of the 

 perithecium surrounding the reproductive 

 organs. They germinate to produce fresh 

 mycelium (Fig. 243). 



Closely allied to Aspergillus is the genus 

 Penidlliuni, which is used, associated with 

 other Fungi, in the " ripening " of cheese. 

 It differs chiefly from Aspergillus in the 

 form of the conidiophore (Fig. 244). The 

 conidiophores are narrow and branched and 

 not swollen at their tips, while the coni- 

 diospores are abstricted in more or less 

 parallel chains. The sexual reproduction is 

 similar to that of Aspergillus. The well- 

 known antibiotic substance Penicillin is a 

 product of Penicillium notatum. 



r 



f 



Fig. 244. — PenicUlhun sp. Branched 

 conidiophore with conidjospores 

 abstricted in chains. 



Erysiphales 



The Erysiphales are Ascomycetes which 

 are characterized by an abundant mycelium, 



