270 



Mycologia 



sterigma of half this diameter (Fig. 7-9). Conidial chains may 

 attain a length of 85^, easily break apart in water mounts and 

 do not form columns. Conidia are ovate, elliptical or globose, 

 2.5-4//, by 1.8-2.5 /x in six-day old drop cultures, have smooth 

 walls and appear hyaline under the microscope (Fig. 16, 17). 

 However, when they form in profusion, as infrequently happens 

 in small areas, the surface appears gray with a faintly perceptible 

 shade of green or brown according to the density of the growth. 

 They swell and produce one to three tubes in germination. 



If cultures on steamed rice and potato plugs in tubes, or on 

 potato- and bean-glucose agar in petri dishes, are kept at 35 de- 

 grees Centigrade, great numbers of perithecia will be found de- 

 veloping at the end of two weeks. If crushed mounts are made 

 at the end of 20 days, great numbers of asci and ascospores may 

 be found in all stages of development. Perithecia are at first 

 white, and may remain so ; but, within thirty days, the color may 

 have changed so that white, cream, pink and yellow shades may 

 appear, all of which may be present in the same culture. The 

 yellow is often transitory, fading again to cream or white. 



Perithecial formation begins with the twisting together of the 

 ends of two or more hyphae to form a knot (Fig. 19). Other 

 hyphae grow out from and weave around this knot, gradually 

 enlarging it and forming a white hyphal gnarl. When this gnarl 

 has nearly attained mature size, the cells of the hyphal branches 

 within swell and are transformed to asci (Fig. 23-28). When 

 this process of development is complete, the perithecial cavity is 

 found to be closely packed with ascospores, the delicate ascus 

 walls and all hyphae having entirely disappeared. Perithecia 

 are spherical, except when crowded, 0.4-2 mm. (mostly 0-5.1 

 mm.), indehiscent, with a peridium consisting of three parts: a 

 thin inner layer of closely woven hyphae, a thick middle layer of 

 loosely woven threads, and a very narrow outer layer (Fig. 

 20-22). The hyphae constituting the middle layer and the outer- 

 most layer of the peridium are of less diameter than those com- 

 posing the innermost layer and the ascogenous center. 



Asci are globose, elliptical, or pyriform, 7.2-10.8 by 6.3-7.7 /*> 

 hyaline, 6-8-spored, the walls disappearing as the spores mature 



