482 A MANUAL OF THE PENICILLIA 



limited rot when inoculated into pomaceous fruits, and members of the 

 series are occasionally isolated from natural infections of this kind. Rather 

 close relationship to the P. expansum series appears indicated, since strains 

 apparently intermediate between the two series are sometimes encountered. 

 They are not, however, encountered as a cause of economic losses in apples 

 and related fruits. 



Definite color differences usually serve to differentiate between the 

 Penicillium viridicatum series and P. ochraceum (Bainier) Thom. How- 

 ever, colonies of the latter (consistently in certain strains and in occasional 

 sector variants of almost any strain) may show dull, olive-green to brown 

 colors definitely suggestive of some members of the P. viridicatum series. 



A number of species apparently assignable to the Penicillium viridica- 

 tum series have been described (Thom, 1930), and individual strains can 

 be found which seem to duplicate most of them with reasonable exacti- 

 tude. Such differences as occur, however, are often found to assume minor 

 significance when large numbers of isolates are observed. Characters 

 which may appear clearly diagnostic when four or five strains are examined 

 are found to intergrade and show progressive change when the comparison 

 is extended to many cultures. Of the several species that have been de- 

 scribed, we believe that three can be recognized within the series, as 

 indicated in the key above. 



Of these species, Penicillium viridicatum Westling is the most widely 

 distributed and the most representative. It is characterized principally 

 by bright yellow-green colors usually associated with a marked fascicula- 

 tion of conidiophores. Colonies of P. psittacinum Thom show a similar 

 pigmentation, and this species may be more nearly related to P. viridica- 

 tum than is indicated by the placement given the two species in this Man- 

 ual (see p. 448). Penicillium psittacinum, in its typical aspect, shows a 

 funiculose arrangement of aerial hyphae but no definite upright bundles of 

 conidiophores such as characterize the Fasciculata. Penicillium olivino- 

 viride Biourge usually produces less fasciculate colonies, which on Czapek 

 quickly develop dull olive to gray and on steep agar purplish or vinaceous 

 shades. Penicillium palitans Westling, as understood by us, grows some- 

 what more rapidly than either of the preceding species and quickly de- 

 velops dark rather than bright yellow-green shades which are usually per- 

 sistent in age. This last species is regarded as somewhat transitional in 

 the direction of the P. expansum series. 



Penicillium viridicatum Westling, in Arkiv for Botanilc 11: 53, 88-90, figs. 

 14 and 56. 1911. Thom, The Penicillia, p. 394. 1930. 



Colonies on Czapek's solution agar (Col. PI. VIII) generally restricted, 

 usually attaining a diameter of 2.5 to 3.5 cm. in 12 to 14 days at room 



