CHAPTER XV 



PLECTASCALES 



This group resembles the JSpermophthoraeeae and differs from the other 

 families of the Endomycetales in that the zygote lirst develops ascogenous 

 hyphae which then proceed to the formation of asci and ascospores. The 

 Pleetascales are distinguished from the higher groups of Ascomycetes by hav- 

 ing the asci born in tangled wefts of partially differentiated hyphae. Where 

 a more compact fructification (perithecium) is present, it lacks an ostiole and 

 its asci are irregularly scattered throughout the inner tissue. The outer wall 

 of the perithecium is usually composed of pseudoparenchyma which degen- 

 erates or decays, liberating the mature ascospores. Of the five or six families 

 into which this group is generally divided, we need discuss only three : the 

 Gymnoascaceae, the Aspergillaceae, and the Onygenaceae. The more elaborate 

 fructifications of the other families need further study before their relation- 

 ships will be altogether clear. Dodge (1929) followed the traditional arrange- 

 ment, more or less confirmed by Emmons & B. 0. Dodge (1931) and questioned 

 by Nannfeldt (1932). 



GYMNOASCACEAE 



The simplest member of this group whose morphology and cytology have 

 been studied is Amauroascus verrucosus (Dangeard 1907) usually found on 

 dung as a white, arachnoid covering. Occasionally it thickens to small white 

 knots, the fundaments of fructifications. The multinucleate copulation 

 branches may develop from any two hyphae (Fig. 71, 1, 2). The antheridium 

 (male) is vertical and somewhat the larger; the slenderer ascogonium (fe- 

 male) coils in a helix about the antheridium. Neither cytoplasmic fusion nor 

 nuclear migration has yet been reported. The ascogonium continues to grow 

 (Pig. 71, 3 and 4), putting forth many branches which coil helically (Fig. 

 71, 5) and eventually divide into binucleate cells that swell to 8-spored asci 

 (Fig. 71, 6, 7). Meanwhile a more compact, sterile tissue surrounds the knot 

 of ascogenous hyphae. The asci are then embedded in a loose, brownish hyphal 

 cushion which shows no differentiation of a wall. 



When Arachniotus candidus is cultivated on Pollaeci agar, it fails to form 

 perithecia and resembles the Trichophytoneae in many microscopic details 

 (Pollaeci 1925). 



In Gymnoascus, the hyphal sheath shows a more marked peridial character. 

 This genus is saprophytic on earth, dung, cadavers, offal, etc., where it forms 

 a fluffy, occasionally bright-colored covering. The slender hyphae are divided 



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