OBSERVATION AND DESCRIPTION OF PENICILLL\ 43 



bers of fruiting structures. This can often be done most readily by direct 

 examination of the colony in the petri dish. Habit sketches, made with 

 the aid of a camera lucida, showing the relative size of penicilli, the types 

 of branching observed, and the arrangement of the conidial chains can be 

 very useful. 



In describing species, or in the identification of unknown strains, the 

 type of penicillus most commonly produced must be determined since 

 allocations to major sections are made upon this basis. 



Penicilli are regarded as monoverticillate if each terminal branchlet, 

 with its cluster of sterigmata and conidial chains, seems to stand out 

 separately (fig. 8). Such penicilli may be strictly monoverticillate, i.e., 

 borne upon separate conidiophores which arise either from within the 

 substratum or from trailing vegetative hyphae; or they may be ramigen- 

 ous, i.e., borne as an irregular series of branches at various levels upon a 

 common fertile hyphae. In some forms conidial structure seems to con- 

 sist of terminal groups of monoverticillate heads, but these can best be 

 assigned to another section, usually the Divaricata. 



Penicilli are regarded as biverticillate if branching occurs at two or 

 rarely more than three levels. Such penicilli may be either sjTnmetrical 

 or asymmetrical. If the two groups of branches are regularly and evenly 

 spaced about the central axis, the penicillus is regarded as biverticillately 

 symmetrical, and is characteristic of a major section of the genus, the 

 Biverticillata-SjTnmetrica (fig. 10). If the penicillus appears to be asjon- 

 metrical, one-sided, or lop-sided, the strain or species belongs among the 

 Asymmetrica, in which the branches are characteristically alternate, or 

 form incomplete whorls about a central axis (fig. 9). 



A few species have been described by Bainier (1906-1907) with penicilli 

 several times verticillate below the level of the sterigmata. While these 

 forms doubtfully represent true Penicillia, they are recognized as consti- 

 tuting a section, the Polyverticillata, since they are occasionally encount- 

 ered and superficially at least, closely resemble Penicillium (see Chapter 

 XIV). 



In any case the description should indicate the arrangement of parts, 

 the general pattern, and the number of series or levels in the branching 

 system that appear to be most characteristic of the species or strain under 

 observation. Many difficulties will be encountered, and of necessity much 

 depends upon the experience and judgment of the individual worker. 

 Reduced conidial structures can be found in every species and strain of 

 Penicillium. Generally, however, such reduced penicilli are few in num- 

 ber in the non-monoverticillate sections. In describing the penicilli in 

 any given strain or species it is almost axiomatic that one should observe 

 and record the maximal pattern of penicillus development. Whereas 



