620 MEDICAL MYCOLOGY 



Brefeldianum, and Scopulariopsis alhonigrescens (Acaulium albonigrescens), 

 the ascogenous hyphae divide without resting periods into binueleate cells which, 

 with the fusion of the nuclei, except in P. javafiicum and P. Brefeldianum, de- 

 velop into asci. The ascogenous hyphae gradually digest the inner layers of 

 pseudoparenchyma of the fructification and thus provide the nourishment for 

 the developing ascospores. The mature perithecia consist of a more or less 

 solid pseudoparenchymatous sheath filled with a brownish spore powder. They 

 generally open at the top by disintegration of the upper portion of the peri- 

 thecial wall. In Aspergillus nidulans, the fructifications arise not on the 

 mycelial mat but in special bladder-like sheaths. These sheaths are formed by 

 the cessation of branching of the hyphae next the mycelial covering. The end 

 cells of the ultimate branches swell and thicken their membranes. 



The ascospore of Aspergillus, by a secondary thickening of its cell wall, 

 develops as two symmetrical valves, suggesting the arrangement found in the 

 valve of a bivalve mollusk. The ripe ascospores are commonly shaped as a 

 double convex lens with the valves more or less closely in contact at the edges. 

 A series of variations is possible as shoAvn in Fig. 99. If the exospore is in close 

 contact at all points and the valves are brought together, we find the condition 



Fig. 99. — The ascospores of Aspergillus. 1-1, optical section of the ascospores viewed 

 from the edge (girdle view) ; 8, same, viewed from the top (valve view) ; 1, spore without 

 frill or furrow; 2, spore with single frill at union of the valves in A. pseu.donidulans ; 3, spore 

 with valves slightly .separated, with race of furrow and two frills ; i, valves separate, furrow 

 evident and frills broad as in A. herbariorum ; 5, furrow and frills evident with exospore 

 thrown into folds on the convex faces of the valves, as in A. nidulans and A. Fischeri; 6, valves 

 further separated, f lills reduced to traces, and furrow scarcely visible ; 1, neither frill nor fur- 

 row visibly present, but valves separated ast in A. repens. 



shown in Fig. 99, J; a loose fold of exospore at the line of contact of the valves 

 gives Fig. 99, 2, as in Aspergillus pseudonididans ; if the valves remain slightly 

 separated and a fold of exospore develops at each margin we find the condition 

 shown in Fig. 99, 3, 4, as in the A. herhariornm group ; if the exospore is further 

 thrown into folds or wrinkles on the surface of the A'alves, we find the spores 

 of A. ecJiimdatus, A. nidulans, and A. Fischeri (Fig. 99, 5) ; if the folds are 

 reduced or absent, we see the spores of the A. repens series (Fig. 99, 6, 7). At 

 germination the ascospore swells, the valves first separate along one edge, then 

 after complete separation remain attached to the opposite sides of the spore 

 for some time. In Penicillium Brefeldianum the valvelike nature of the spore 

 wall is seen only in germination. 



Sclerotia, hard masses of mycelium with characteristic surface markings 

 and colors, occur in several groups of species in Aspergillus and Penicillium. 

 These consist largely of pseudoparenchyma and have probably often been mis- 

 taken for perithecia. 



