26 



STRUCTURE AND CLASSIFICATION OF FUNGI 



times divided into three more or less well defined subclasses. In the 

 first, the Plectomycetes, the asci are scattered on the ascogenous 

 hyphae and are consequently distributed irregularly inside the peri- 

 thecium, like Aspergillus (Eurotium). See Fig. 48. In the second 

 subclass, the Discomycetes, the asci are borne in palisades, a hy- 

 menium, in an open cup or plate-like apothecium, like in Peziza 

 (Fig. 15) . In the third or Pyrenomycetes the asci are contained in 



a hymenium in perithecia as in 

 Claviceps (Fig. 21). See page 

 33 for key to subclasses of 

 Ascomycetes. 



It must be emphasized that 

 there are literally hundreds of 

 species and scores of genera of 

 Ascomycetes the life cycles of 

 which for the most part have 

 not been worked out. The 

 cycles of some of them, how- 

 ever, have been worked out as 

 completely as that of Claviceps 

 purpurea, which has been taken 

 as an example. One may find 

 excellent material for micro- 

 scopic wet mount study of 

 ascospores in the common sap- 

 rophyte Peziza in the spring, 

 or powdery mildews of a num- 

 ber of plants, e.g., lilac, late in the summer or early autumn. 

 Dried material of either will yield very satisfactory preparations 

 when wetted. The ascospores of yeasts, Aspergillus, and other forms 

 of special interest to the bacteriologist will be considered later. 



Fungi Imperfecti. There are many fungi which possess the char- 

 acteristic mycelium of Ascomycetes, which reproduce by conidia sim- 

 ilar to those formed by known Ascomycetes, yet which do not form 

 ascospores, or whose ascospores have not yet been discovered. These 

 are designated imperfect fungi, or Fungi Imperfecti. It must be con- 

 fessed that probably in many cases the imperfection lies in our knowl- 

 edge of the organism rather than in the organism itself. They must be 

 classified and identified by their conidia. Although the Fungi Im- 

 perfecti have been established as a class equal in rank to the Basid- 

 iomycetes, Ascomycetes, and Phycomycetes, it should be recognized 

 that an attempt is continually being made to classify the latter three 



Fig. 20. Stained section of a stroma of 



Claviceps purpurea showing numerous 



perithecia at the periphery. 



