KEY TO THE GENERA OF FAMILY ERYSIPHACEAE 353 



The female gametangium enlarges and the male gametangium sends a 

 conjugation tube into it. Numerous male nuclei and some cytoplasm 

 enter the oogone, whose nuclei divide several times as do the introduced 

 male nuclei. Many nuclei of both sexes degenerate but many pairs of 

 uniting nuclei are found. Around each such zygote nucleus is organized a 

 mass of cytoplasm, called by the investigator an "egg." There is no cell 

 wall between this egg and the rest of the protoplasm. The number of such 

 zygote nuclei and eggs varies, usually being large but being reduced to 

 one in rare cases. Each zygote nucleus divides several times and the egg 

 cytoplasm undergoes cleavage until as many spores are formed as there 

 were nuclei produced. Spore walls are formed and within the gametangium 

 are now found as many spore balls as there were uniting pairs of nuclei. 

 Varitchak called each ball of spores an ascus and the whole structure a 

 "synascus." By reduction of the number of uniting nuclei and resultant 

 spore balls a condition would be attained, according to him, similar to 

 that in Dipodascus whose ascus he calls a "hemiascus." By reduction of 

 the number of nuclei in the uniting gametangia to one in each as in 

 Endomyces a true ascus would be formed. (Fig. 118.) 



Key to Families of Order Erysiphales 



Aerial mycelium hyaline. Outer colored layer of perithecial wall one cell in thick- 

 ness, of polygonal cells, brittle. Family Erysiphaceae 

 Aerial mycelium (when present) dark. Outer peridium layer not brittle. 



Peridium parenchymatous, not slimy; mycelial hyphae cylindrical, not slimy. 



Family Meliolaceae 

 Peridium dissolving into slime; mycelial hyphae moniliform or cylindrical. 



Family Englerulaceae 

 Perithecium walls built of moniliform or cylindrical hyphae, more or less slimy. 

 Mycelium moniliform or cylindrical, united in strands. 



Family Capnodiaceae 

 MyceUum dark-colored, parasitic on epiphyllous Meliolaceae and similar fungi. 

 Perithecium inverted at maturity, with the morphological base upward. 



Family Trichothyriaceae 

 Forming rounded or stellate cushions on leaves, gelatinous when wet, horny 

 when dry, with no free mycelium. Asci scattered in thickened area of the 

 thallus. Family Atichiaceae 



Key to the Genera of Family Erysiphaceae 



Ascospores one-celled. 



Perithecia normally containing only one ascus. 



Appendages hyplia-like, usually unbranched. Sphaerotheca 



Appendages stiff, dichotomously forked at tip. Podosphaera 



Perithecia normally containing several to many asci. 



Appendages hypha-like, mycelium external, conidia in chains. 



Erysiphe 

 Appendages hypha-like, mycelium internal as well as somewhat external, 

 conidia falling off singly, sometimes producing short chains. 



Leveillula 



