ASCOMYCETES 



35 



developed. In this way a single species may have four or five 

 forms of spores, with different shapes, functions, methods of pro- 

 duction and periods of germination. In some instances the conidia 

 are produced on one host and the ascocarps on another, the 

 former being frequently parasitic and the latter saprophytic. A 

 large number of conidia- and pycnidia-bearing species is known 

 whose relation to ascus-bearing species is unknown ; in some 

 cases it is probable that the ascosporic condition does not exist. 

 These forms have commonly been called Fungi iinperfecti from 

 their real or apparent resemblance to the conidial and pycnidial 

 forms of ascus-bearing fungi. It is more than probable that many 

 forms that have been classified in this convenient catch-all are 

 species perfect in themselves. 



Counting the Fimgi impcrfixti there are seventeen orders of 

 Ascomycetes all but one of which are well represented in 

 America.* These orders may be distinguished by means of the 

 following synoptical table : 



1. Asci separate from each other, not uniting in a special perithecium or 



ascoma, and without a special covering. 2. 



Asci grouped or fasciculate, surrounded by a spherical, cylindric or 



pyriform shell or perithecium, 3. 



Asci collected in a hymenial layer, remaining enclosed in a tuber-like 



ascoma; habit subterranean. (Truffles.) 10. Tuberales. 



Asci collected in a flattened or concave hymenial layer (ascoma) often 



bordered by a disdnct layer. (DiscoMYCETES.) 8. 



2. Asci entirely isolated or fonned at different parts of the mycelium which 



is often undeveloped ; vegetative reproduction accomplished by gem- 

 mation. (Yeast plants. ) 2. Saccharomycetales. 

 Asci approximate and forming an indefinite hymenium. (Our forms 

 are mostly parasitic, deforming their hosts, forming bladder plums, 

 leaf curls, etc. ) 3. Exoascales. 



3. Perithecia borne on a short pedicel ; microscopic fungi parasitic on bee- 



tles and other insects. 9. Laboulbeniales. 



Perithecia sessile, either solitary and free, or united and imbedded in a 



stroma. 4. 



*The Protomycetales [Hemiasci) are low forms of fungi with usually 

 a many-spored ascus. Of these, one form, Protomyces polysportis, has been 

 reported from this countiy parasitic on Ambrosia trifida. For literature on 

 the three families of this order see Schroeter, loc. cit. 143-149. 



