132 



PLANT MORPHOLOGY 



behavior may be repeated a number of times. Each cell in which a 

 nuclear fusion occurs may become an ascus, the fusion nucleus under- 



FiG. 107. Ascocarps of Peziza growing on decaying wood, natural size. 



going the usual three successive divisions to produce eight ascospore 

 nuclei. The significance of hook formation, which occurs in many 



Ascomycetes, is a puzzle. 



Peziza. Peziza is one of the best-known 

 cup fungi, including about 150 species. It is 

 a common saprophyte on rich humus or on 

 decaying wood. The mycelium, which is ex- 

 tensive and much branched, penetrates the 

 substratum and gives rise on the surface to 

 smooth, fleshy, cup-like ascocarps 1 to 5 cm. 

 or more in diameter (Fig. 107). These are 

 generally bright red, brown, or gray. As in 

 Pyronema, the ascocarp is lined with a layer 

 of parallel asci and paraphyses, these consti- 

 tuting the hymenium (Fig. 108). Each ascus 

 contains eight ascospores. Upon germination, 

 these produce new mycelia. In Peziza the 

 ascocarp apparently arises directly from the 

 mycelium without any formation of sex organs. 

 Sclerotinia. A parasitic cup fungus, Sclero- 

 tinia fructicola, attacks plums and peaches, 

 causing a disease known as brown rot of stone 

 fruits. The twigs, flowers, and fruits become 

 infected with the mycelium. As the fruit turns brown and decays, great 

 numbers of conidia are formed on the surface. These are cut off in chains 

 from the ends of short conidiophores. The conidia carry the fungus to 



Fig. 108. Several mature 

 asci of Peziza, each with eight 

 ascospores, intermixed with 

 paraphyses, X 250. Some 

 young asci are arising below. 



