ASYMMETRICA-DIVARICATA 293 



This was isolated by Dr. H. Schnegg in Weihenstephan from hops, was 

 sent to us by Westerdijk in 1938,' and subsequently was described by van 

 Reyma in 1939. A new culture of this strain has recently been received 

 from the Centraalbureau. The two cultures duplicate one another in cul- 

 tural characteristics but cellular elements of the penicilli tend to be some- 

 what smaller in the latter substrain and to fit van Beyma's original de- 

 scription better than those of NRRL 872. The identity of the two 

 cultures, however, is unmistakable and the present description is drawn 

 sufficiently broad to include both substrains as they now exist. 



The cultures under study both stem directly from van Beyma's type but 

 in our experience have never shown any yellow-green color such as de- 

 scribed for the species by him. His notes were made from cultures grown 

 on beer-wort agar and the possibility exists that coloration of colonies on 

 this medium would differ from that upon the substrata which we have 

 employed. This is questioned, however, since we have grown the mold 

 upon a variety of media, including malt extract, without any suggestion 

 of green. 



Thom examined this culture prior to its description by van Beyma and 

 suggested placing it in his Lanata-Divaricata group (1930) near Peni- 

 cillium lilacinum. Van Beyma accepted this disposition but called atten- 

 tion to certain cultural features, notably the "powdery" rather than 

 floccose surface of the colonies, which did not conform with the typical 

 characters of this group. The validity of van Beyma's exceptions is 

 recognized although colonies on malt tend to develop a fibrous or lightly 

 flocculent surface. Furthermore, the penicilli commonly appear mono- 

 verticillate, or do not normally branch at a number of different levels as in 

 P. lilacinum, the sterigmata are not usually characterized by pointed conid- 

 ial tubes as in the latter species; and the conidia are more nearly sub- 

 globose than elliptical. Despite these differences, we believe the total 

 cultural and morphological picture of P. humuli enables it to be keyed 

 with the P. lilacinum series more satisfactorily than elsewhere. 



Tan Mutants of Other Species 



Strains which superficially resemble Penicillium humuli van Beyma 

 in color and to a lesser degree in general cultural appearance, are occa- 

 sionally observed as sector variants in colonies of other species. In the 

 present study, such tan mutants have been observed in, and isolated from, 

 normal green or blue-green colonies of both P. spinulosum Thom, in the 

 Monoverticillata, and P. rugulosum Thom, in the Biverticillata-Symmet- 

 rica. Examination of conidial structures in both ca-^es promptly and un- 

 mistakably confirmed their identity as mutants differing from the parents, 

 principally in conidial color. Tan-spored cultures are occasionally iso- 



