MICRO-ORGANISMS 11 



forms as the Hemiascomycetes, or it may be grouped with others in 

 fruit bodies, or ascocarps, of varying complexity. The young ascns 

 typically starts out as a binucleate cell, in which the nuclei fuse, divide 

 meiotically, and redivide, forming in most species eight haploid asco- 

 spores by the process called free-cell formation. 



The number of ascospores is usually constant within a species, but 

 the number per ascus varies within the class from one, as in Tuber 

 candid-um Harkn., to more than a thousand (rare), as in Thelebohis 

 stercoreus Tode ex Fr. (3). The asci containing fewer spores than 

 eight, as in the Saccharomycetaceae, are sometimes considered reduced 

 forms; those containing more than eight, as in the Dipodascaceae, 

 often are considered somewhat primitive forms. 



Asexual reproduction in the Ascomycetes is common and usually 

 comprises one or more of the conidial types found in the class Fungi 

 Imperfecti. E?nericellopsis, for example, has a conidial state classi- 

 fiable in the form genus Oephalosporium; Microascus has the Scopu- 

 lariopsis type ; and Byssochlamys has the Paecilomyces type. Ceralo- 

 cystis galeiformis Bakshi has three conidial types — Leptographium. 

 G-raphium, and Oephalosporium. Some ascomycete genera have 

 conidial types that would be classifiable in a single genus of the Fungi 

 Imperfecti. Gibberella, Nectria, Hypomyces, and Calonectria have a 

 Fusarium type of conidial apparatus ; Eurotium, Sartorya, and Eraeri- 

 cella all have an Aspergillus type; and both Physalospora. a pyreno- 

 mycete, and Tryolidiella, a discomycete, have a Diplodia type. 



Conidial states often are inconspicuous where associated with the 

 ascocarpic or perfect state on natural substrate, but may predominate 

 or even be the only state present in culture. Eurotium is one of the 

 cleistothecial genera with the Aspergillus type of conidial apparatus. 

 It was reported as Mucor lierbariorum on natural substrata as early as 

 1780 by TViggers, but no association was made with a conidial state 

 until 74 years later when DeBary (<§), interested in life cycles, proved 

 that its conidial state was an Aspergillus. 



Some strains in culture are sensitive to substrate and temperature 

 changes, and under proper combinations of conditions they vary from 

 being almost entirely cleistothecial to being entirely conidial. This 

 classification does not mean, however, that the name Aspergillus can 

 be abolished or removed from its proper placement in the Fungi Im- 

 perfecti, because numerous species apparently do not have perfect 

 states and may never have. Neither can the ascomycetous genus or 

 species in which such strains would belong, if they formed perfect 

 states, be predicted with any degree of certainty. 



The Ascomycetes are classified primarily on the basis of the mor- 

 phology and development of their sexual states. The early classifi- 

 cational systems emphasized gross morphology, whereas later treat- 

 ments stressed the nature of the asci and other microscopic structures. 

 Traditionally the class is divided into two main groups or subclasses, 

 the Hemiascomycetes, containing yeasts and other families that do 

 not produce their asci in ascocarps, and the Euascomycetes, contain- 

 ing the balance of the class that does form ascocarps. 



Due partly to the size of the class, there are no recent comprehen- 

 sive taxonomic treatments of the species. However, Martin { . 

 presents a key to families, and Bessey (3) gives keys to families and 



