ASYMMETRICA-VELUTINA 



359 



biologist soon comes to recognize so that valuable strains can be maintained 

 without great difficulty. H 



Members of the Penicillium chrysogenum series appear to be unusually 

 long-lived. Thom (1930) reported a culture as viable after 8 years in a 

 laboratory test tube. In a series of viability tests made in 1945 on test- 

 tube cultures that had been brought to Peoria five years earlier, members 

 of this series, almost without exception, were still viable and produced 

 colonies characteristic of the various strains tested. This was not equally 

 true of any other series of the Penicillia. It was approached only by the 

 P. purpurogenum and P . funiculosum series in the Biverticillata-Symmetrica 

 where approximately 50 per cent remained viable. As a matter of fact, 

 the longevity of conidia in dry test-tube cultures has upon occasion pro- 

 vided valuable indications of true relationships in isolated cases where 

 strains had been incorrectly diagnosed. 



The separation here proposed is far from ideal, but it is believed to be 

 workable in the vast majority of cases. Fortunately, for many types of 

 investigation, including the search for improved penicillin producing molds, 

 identification to the series is sufficient — high yielding strains may belong to 

 either P. notatum or P. chrysogenum. The species selected for recognition 

 can be expected to serve principally as guide-posts in a great series of inter- 

 grading strains. Seldom will they offer the worker assurance that he has 

 rediscovered the exact organism described by an earlier investigator. 



Penicillium chrysogenum Thom, in U. S. Dept. Agr., Bur. Anim. Ind., Bui. 

 118, pp. 58-60, fig. 20. 1910; Thom, The Penicillia, pp. 261-262. 1930. 

 See also Biourge, Monograph, La Cellule 33: fasc. 1, pp. 170-172, Col. 

 PI. IV and PI. VI, fig. 32. 1923; and Westling, Arkiv f. Bot. 11: 54, 

 107-108, figs. 23 and 64. 1911. 



Colonies on Czapek's solution agar growing rapidly, attaining a diameter 

 of 4.5 to 5.0 cm. in 10 to 12 days at room temperature, consisting of a com- 

 paratively thin basal felt bearing crowded conidial structures, in some 

 strains closely velvety (fig. 95A), in others deeply velvety and rather loose- 

 textured (fig. 95E), usually azonate, typically showing conspicuous radial 

 furrows which lend to the colony a wheel-like appearance, comparatively 

 deep, up to 1 mm. or more in some strains, thin in others, not exceeding 

 300-500m, with growing margin 1 to 2 mm. wide, white; heavily sporing 

 throughout in most strains, in others often showing some tendency to re- 

 main sterile in central areas with vegetative mycelium yellowish to cream 

 colored, conidial areas in yellow-green to bluish gray-green shades, in some 

 strains ranging from pistachio green to American green (Ridgway, PI. XLI) 

 becoming blue-green near Russian green or dark Russian green (R., Pi. 



