652 A MANUAL OF THE PENICILLIA 



Penicillium tardum. These cultures may or may not have stemmed from 

 the same original source. The species is approximated by NRRL 1052 

 (Thorn's No. 4640.439), received in 1922 from the Bainier Collection as 

 P. atricolum. 



The above strains show definitely roughened conidia and, since one of 

 these represents type material, it is assumed that the conidia in Thom's 

 cultures were also rough, although this was not specifically stated. Several 

 additional strains approximating the above have been examined in the 

 current study. Others differ from them in producing conidia with heavy 

 walls that are smooth or nearly so and colonies on malt agar in darker 

 yellow-green shades. These latter forms are regarded as best considered 

 with the species PemciUium tardum, and it is possible that the species de- 

 scription should be broadened to include forms with both rough and smooth 

 conidia. NRRL 2117 is representative of the forms with almost smooth 



conidia. 



Thom (1930) based his species Penicillium tardum upon a culture re- 

 ceived from the Bainier Collection (Thom's No. 4640.444— NRRL 1073) 

 as P. elongatum Bainier. Because of the prior use of that name by Dierclcx 

 for a different type of Penicillium (belonging to the P. expansum series, 

 q.v.), Thom redescribed the species and, because of its slow development on 

 Czapek's agar, applied to it the name P. tardum. Development of the 

 species on other media was not discussed. 



As newly isolated from nature, strains of Penicillium tardum typically 

 produce very thin and somewhat restricted colonies on Czapek's agar with 

 almost all vegetative mycelium submerged and conidial structures spar- 

 ingly produced, and with these nearly always arising directly from the sub- 

 stratiun. Strains long maintained in laboratory culture, such as NRRL 

 1073, commonly show a limited adaptation to synthetic media and gradu- 

 ally develop progressively larger and more flocculent colonies in which the 

 marginal area only may retain the original appearance. 



In the period since Penicillium tardum was described, it has been com- 

 mon practice in this Laboratory to assign to this species all strains that 

 grow sparsely on Czapek's solution agar and produce typical biverticillate 

 and symmetrical penicilli. As nutrient deficiencies have become better 

 understood as factors affecting rates of growth and colony appearance in 

 the Penicillia, some cultures previously assigned here have been foimd to 

 represent deficient strains of other species of the Biverticillata-Symmetrica 

 which are incapable of elaborating necessary amino acids, enzymes, or vita- 

 mins. Before assigning a strain to P. tardum, therefore, every possible 

 effort should be made to identify whatever deficiency is responsible for its 

 limited or restricted growth. If a deficiency is found, the strain, when 

 grown upon non-deficient media, should be carefully compared with other 



