ASYMMETRICA-VELUTINA 405 



and numerous strains in our possession have come from decaying fleshy- 

 fungi of one type or another. 



This series is characterized particularly by the comparatively short and very 

 compact base of the penicillus. Typically this consists of a compact verticil 

 of metulae and crowded sterigmata borne upon the main stem and upon 

 one or more lateral branches that arise from the next lower node, but remain 

 closely appressed against the main stem as illustrated in fig. 106. Branch- 

 ing within the penicillus is often irregular, and differentiation between the 

 metulae and the branches or sub-branches which support these is often 

 difficult to establish. Occasionally the structure may branch and rebranch 

 at 3 or 4 levels below the sterigmata in at least a portion of the penicillus. 

 On the other hand, in most members of the series, a considerable proportion 

 of the penicilli are unbranched and show only a single terminal cluster of 

 metulae bearing crowded sterigmata, and in some strains this type of peni- 

 cillus occurs almost to the exclusion of the more complexly branched struc- 

 tures (fig. 108). In most members of the series the larger and more char- 

 acteristic penicilli are typically borne upon conidiophores arising from the 

 substratiun, whereas the smaller and less characteristic structures are com- 

 monly borne upon aerial hyphae. In all forms the sterigmata are closely 

 compacted at the base and may either diverge at their apices or remain 

 essentially parallel. Conidial chains arising from the same penicillus are 

 often of variable length and usually appear loosely parallel or divergent. 

 There is little or no tendency toward column formation, and in age the 

 conidial chains characteristically form a tangled mass (fig. 106). Viewed 

 under low power, the typical penicillus is in every sense a compact brush- 

 like structure (fig. 107E), hence the appropriateness of Dierckx's name Peni- 

 cillium brevi-compactum. 



Members of the series characteristically show stolon-like aerial hyphae 

 which extend beyond the growing margin and return to the substratum 

 (fig. 107F), especially when cultivated under very humid conditions, or upon 

 especially moist substrata. In his original strain, Thom supposed this 

 character to be diagnostic, hence applied the name PenicilUum stoloniferum 

 (1910) to a form which exhibited this tendency in striking manner. Sub- 

 sequently it was recognized that the development of stolon-like hyphae 

 represented a group characteristic rather than a specific one since it occurs 

 in almost all members of the series. The structure of the penicillus appears 

 to be a much more stable character than stolon production, which was 

 originally thought to be significant. In the meantime, the prior but inade- 

 quate description of one of these forms by Diercloc (1901) under the ex- 

 ceedingly descriptive binomial, PenicilUum brevi-compactum, came to 

 Thom's attention. In recognition of this fact, Thom (1930) subsequently 

 applied the designation "The Brevi-Compacta" to the series represented by 



