588 A MANUAL OF THE PENICILLIA 



mata tapered in the manner characteristic of the group, produced in hmited 

 ckisters up to 6 or 7, variable in dimensions, 8 to 12iJ. by 2.0 to 2.5m, bearing 

 conidia in short divergent chains; conidia elhptical, smooth, about 3.0 to 

 3.5m by 2.5m. 



Colonies on malt extract agar spreading broadly, up to 6 to 7 cm. in 

 12 to 14 days, plane (fig. 150B), comparatively thin, consisting of a loose 

 network of aerial mycelium in which soon develop abundant perithecia 

 with accompanying encrusted and pigmented hyphae to give the colony 

 a rich golden yellow color, in age near light cadmium to aniline yellow 

 (Ridgway, PI. IV) ; conidial structures lacking or limited in number, odor 

 lacking; no exudate; reverse in brownish orange shades; perithecia gener- 

 ally spherical or nearly so (fig. 150C), ranging from 100 to 300m in diameter, 

 usually about 200 to 250m, soft, sometimes confluent, without specialized 

 cellular walls but bounded by thin interwoven hyphal networks, and sur- 

 rounded by loose coverings of twisted or spiral, encrusted, and pigmented 

 hyphae up to 150 to 200m or more in length; asci produced abundantly 

 throughout, borne in short chains, at maturity spherical to ovate, 5.5 to 

 7.0m in diameter, 8-spored, ascus walls breaking down quickly to leave the 

 perithecial cavity filled with free ascospores; ascospores small, elliptical, 

 delicately spinulose over the entire surface (fig. 150D), about 2.5 to 3.0m 

 by 1.4 to 1.8m. 



Colonies on cornmeal agar spreading fairly broadly, 5 to 6 cm. in 2 weeks, 

 vegetative mycelium largely submerged and producing scattered perithecia 

 and limited conidial structures, mostly fractional. 



Perithecial initials (fig. 144D) are readily observed upon most substrata, 

 particularly upon cornmeal agar. They first appear as thickened, club- 

 shaped hyphae (ascogonia?) around the bases of which coil much thinner 

 hyphae (antheridia?). These latter hyphae confine themselves to the basal 

 areas of the club-shaped structures and usually terminate as slight enlarge- 

 ments closely appressed against the walls of the larger hyphae. The club- 

 shaped hyphae apparently elongate and soon begin to coil terminally, at 

 first in loose helix-like patterns and subsequently as rather tight spirals. 

 As the spirals continue to develop, their identities are soon lost in develop- 

 ing knots of interwoven tissue. We have not succeeded in establishing 

 whether these knots develop primarily by the septation and repeated 

 branching of the coiled structures or by the proliferation of adjacent hy- 

 phae. The developmental history of the perithecium has not been eluci- 

 dated, but the origin and pattern of ascus formation can be fairly well 

 worked out in the ripening perithecium. 



Species description based upon NRRL 2106 as type; isolated originally 

 from soil from Sweden sent to us by Professor Edy Velander. 



Penicillium helicum is distinguished from other members of the P. luteum 



