MONOVERTICILLATA 155 



2'. Sclerotia in flesh to pink shades, not in clusters and not embedded in masses 



of orange-red hyphae P- thomii Maire 



3'. Sclerotia in orange-brown shades, not in clusters, often surrounded by a loose 



network of yellow to orange or light brown mycelium P. lapidosum n. sp. 



b. Sclerotia produced upon some substrata, not on others including Czapek, com- 

 paratively soft, composed of pseudoparenchymatous cells with walls thickened. 



P. turbatum sub-series 

 r. Colonies on Czapek agar not developing dull dark purple colors in reverse, 



somewhat restricted P- turbatum Westling 



2'. Colonies on Czapek agar developing dull, dark purple colors in reverse, very 

 restricted P- pusillum Smith 



Briefly characterized, the Penicillium thomii series comprises a group of 

 monoverticillate Penicilha which regularly produce sclerotia. As a matter 

 of convenience, the series may be subdivided as follows: (1) the series 

 proper, wherein the member-species produce abundant sclerotia upon all 

 substrata, and the sclerotia are very hard, brittle, and crush with difficulty; 

 (2) the P. turbatum sub-series, in which sclerotia are not produced upon 

 some substrata (including Czapek agar), and the sclerotia are softer and 

 represent less compact masses of thick-walled cells. 



In general appearance, form, and texture the sclerotia of Penicillium 

 thomii and allied species are strildngly similar to those produced by P. 

 raistrickii Smith, a consistently biverticillate species (see p. 275). The 

 degree of relationship between the two series, of which these species are 

 representative, has not been worked out, but there is a definite possibihty 

 that the two will tend to merge as more and more sclerotium-producing 

 strains are examined. At the same time the sclerotia of P. thomii, etc. are 

 strongly suggestive of the late-ripening perithecia of certain ascosporic 

 species such as P. parvum Raper and Fennell (p. 138), in the P. javanicum 

 series, and P. aspenmi (Shear) n. comb. (p. 263), in the Carpenteles series. 

 In early stages of development the perithecia of these latter species are 

 strikingly similar to the sclerotia of P. thomii in form and texture, and re- 

 veal apparent differences only after 3 to 4 weeks or more when asci begin 

 to appear in limited central areas of the previously completely sclerotioid 

 bodies. The process of ripening and attendant ascospore formation may 

 proceed until only a thin outer wall 2 to 3 cells in thickness remains, or it 

 may cease at any time prior to this, and under certain conditions, as yet 

 not adequately explored, it may never be initiated. In the latter case the 

 potential perithecium remains in effect a sclerotium. There are then a 

 number of considerations which seem to tie these different ascosporic and/or 

 sclerotial series together, and it may eventually become desirable to group 

 together into a single section all of the species now regarded as comprising 

 the monoverticillate P. javanicum (ascosporic) and P. thomii (sclerotial) 

 series and the biverticillate Carpenteles (ascosporic) and P. raistrickii 

 (sclerotial) series. 



