116 A MANUAL or THE PENICILLIA 



ual are based upon our own observations of living cultures grown under 

 fairly standardized conditions. Commonly the descriptions are supple- 

 mented by pertinent observations made by the species' author, or other 

 investigators, who may have worked with the species or strains in question. 

 If a latin description was given in the original work, this naturally forms 

 the central core upon which recognition is based, or around which it is at- 

 tempted. Vernacular notes and carefully executed figures often provide 

 additional valuable clues to identity. It is believed that the user of this 

 book will benefit by the presentation of fairly uniform descriptions resulting 

 from broad comparative studies and the presentation of original data in 

 fairly standardized form, rather than by any scheme wherein a maximum 

 amount of the original description might be preserved. In every case we 

 have endeavored to cite the place of species publication in order that the 

 user of the Manual may consult the original paper if needed. 



The standardized species description should specify the substratum and 

 temperature used ; the texture and appearance of the colony, together with 

 marginal features, zonation if present, etc.; color, including color changes 

 in conidial areas, the colony reverse, and the substratum; the presence or 

 absence of odor and transpired drops, and their characterization if possible ; 

 the character of the conidiophore, including its origin, measurement, and 

 wall markings if any; the penicillus, with its branching system, including 

 metulae, and sterigmata; conidia and conidial chains; perithecia or scle- 

 rotia, if present, with whatever distinguishing features they may exhibit; 

 and finall}^, any conspicuous feature of metabolism that is laiown. 



Over a period of many years, we have used Czapek's solution agar (see 

 p. 64) more than any other for the general study of species of PenicilUum. 

 It is readily prepared; it should not differ materially in different labora- 

 tories; its reaction is almost neutral; it is colorless, hence reveals color 

 changes due to the mold growth; and most species of PenicilUum grow 

 moderately well upon it. It is not suitable for the cultivation of perithecial 

 forms, and occasional species and strains which suffer from some nutritional 

 deficiency make at best a very sparse and atypical development upon it. 

 In the current study we have routinely cultivated strains in parallel upon 

 Czapek's agar, Czapek's agar containing one per cent corn steep liquor 

 (termed steep agar), and malt extract agar. The latter medium is espe- 

 cially favorable for ascosporic strains. The addition of the steep liquor to 

 Czapek's agar supplies vitamins, essential amino acids, etc. that are neces- 

 sary for the growth of some forms. 



Varieties 



The taxonomic term variety, is little used in this Manual. Whenever it 

 occurs, it is intended to distinguish some particular strain, or group of 



