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CLASS ASCOMYCETEAE 



and oogone) unite but the contained nuclei do not unite now but wait 

 until the ascus is formed. On the basis of this homology Guilliermond 

 considered the Saccharomycetales to represent a lateral offshoot in which 

 the union of gametangia has become established but in which the sporo- 

 phytic phase has undergone reduction to a single ascus. Thus Dipodascus, 

 Ascoidea, Endomyces, etc., are, according to him, not in the line of evolu- 

 tion to the higher Ascomyceteae which arose more directly from forms 

 intermediate between them and Spermophthora. 



Family Pericystaceae. The only genus recognized is Pericystis, the 

 cause of "chalk-brood" and other troubles in beehives. Two species have 

 been described, apparently both feeding upon the stored pollen in the 

 cells of the comb. The first species described was P. alvei by Miss Betts 

 (1912) and the second was P. apis described by Maassen in 1916. The 

 latter besides feeding upon the pollen appears to attack the larvae in the 

 cells of the comb. It was given careful study by Claussen (1921). The 

 systematic position of this genus is in doubt. Fitzpatrick (1930) placed it 

 among the doubtful Phycomyceteae. Varitchak (1933) who studied the 

 life history and nuclear behavior of P. apis, concluded that it is a primitive 

 Ascomycete related to Dipodascus and Ascoidea but far nearer the sup- 

 posed phycomycetous ancestors. The mycelium, as in Ascoidea, contains 

 chitin and not cellulose. As in that fungus it is septate with multinucleate 

 segments, the septa being centrally perforated, thus permitting the flow 

 of cytoplasm from segment to segment. The mycelia are of two sexes, the 

 fungus being heterothallic. When they come into contact multinuclear 

 gametangia are produced, each separated by its septum from the main 

 hypha. They resemble at first the early stages of conjugation in Mucor. 



Fig. 118. Fungus of uncertain relationship. Family Pericystaceae. Pericystis apis 

 Maassen. (A) Conjugating gametangia. (B) The same, in optical section. (C) Oogone 

 with zygotes. (D) Oogone with zygotes which have produced spores and thereby have 

 become spore balls. (After Claussen: Arh. biol. Reichsanstalt Land- u. Forstw., 10:467- 

 521.) 



