224 CLASS ASCOMYCETEAE 



Order Pezizales. The fungi comprising this order are mostly sapro- 

 phytes although a number of the more or less serious diseases of culti- 

 vated plants are caused by parasitic species (e.g., various species of 

 Sclerotinia, Pseudopeziza, etc.). Those forms that are parasitic do not 

 attack algae in such a manner as to produce lichen thalli. Asexual repro- 

 duction by means of conidia is found in a good many species but is by 

 no means as widely distributed as in some of the orders to be discussed 

 later. Conidia are formed singly on simple or branched conidiophores 

 or the individual cells of whole segments of mycelium may round up to 

 form chains of conidia. In a number of species sclerotia are produced in 

 abundance. 



In this order we find almost all gradations in sexual reproduction. In 

 Stromatinia gladioli (Drayton) Whetzel, it was shown by Drayton (1932, 

 1934) that minute sperm cells must be brought to certain receptive organs 

 of the ascogonia before apothecia can be produced. In Ascobolus car- 

 bonarius Karst., B. O. Dodge (1912) showed that a much coiled asco- 

 gonium bears a long trichogyne which grows toward a structure resem- 

 bling a conidium and attaches itself and fuses with it. This resembles 

 greatly what Miss Bachmann described for Collemodes. In the genus 

 Ascobolus other species have an ascogonium which coils directly around 

 and fuses with an upright antherid (Dodge, 1920). In still other species 

 both Schweizer (1923) and Ramlow (1914) have indicated that antherid 

 and trichogyne are both absent. In Scutellinia stercorea (Fr.) Kunze, 

 according to Miss Fraser (1907), the oogone is rounded and multinu- 

 cleate, as in Pyronema, but the trichogyne is several-celled. S. G. Jones 

 (1930) found in Pseudopeziza trifolii (Biv.-Bernh.) Fckl. the production 

 within the leaf of the host (Trifolium pratense L.) of numerous ascogonial 

 coils made of heavily staining uninucleate cells. Around these but without 

 any visible cell fusion the vegetative mycelium develops into actively 

 growing hyphae, some of which emerge from the stomata. Jones called 

 these "trichogynes" but denied any reproductive function, considering 

 them to be "respiratory hyphae." Other hyphae become true ascogenous 

 hyphae with binucleate cells and still others produce the paraphyses and 

 other portions of the apothecium while the original ascogonium degen- 

 erates without having served any other function than as a center of 

 attraction for the surrounding hyphae. There is a nuclear fusion in each 

 young ascus and only the first of the following three nuclear divisions is 

 reduf'tional. In some Pezizales even the oogone or ascogonium is not to 

 be found. The eventual product is an apothecium which in its general 

 plan is like that of the Lecanorales but usually larger and more fleshy. 

 (Fig. 75.) 



In this order two series of forms may be distinguished, depending upon 

 the mode of dehiscence of the ascus at maturity, viz., the Operculatae 



