Thom: Penicillium Luteum-Purpurogenum Group 137 
Among these forms is one well-marked organism (No. 2670) 
P. purpurogenum var. rubri-sclerotiuni, with all the common 
characters of the series but producing abundant sclerotia, dark- 
red to black in color, upon the surface of the substrata. If these 
sclerotia should be found to be undeveloped perithecia, the form 
would be clearly eliminated from genetic relationship to the forms 
at the luteum end of the series, but would probably take with it 
the other forms at the purpurogenum end of the series. 
Colony Char.-\cters 
The production of yellow in the surface growth at some period 
of colony development or under some cultural conditions is typ- 
ical for the group. This may be dominant, transient, or almost 
lacking yet it is not difficult to demonstrate in the organisms 
studied. Microscopic examination shows this color to be due to 
the encrustment of the aerial hyphae, or part of them, with yel- 
low granules. Definite quantitative differences in this color are 
shown by successive cultures of the same strain in different media, 
especially in media with differing reaction. The different num- 
bers of the series show fairly constant differences in the amount 
of yellow color produced. This quantitative difference is partly 
at least due to the characteristic differences in the amounts of 
surface mycelium produced by the different races. Color in- 
creases with ffoccosity. In P. pinophilmn, Hedgcock^^ found 
that the color of the granule was yellow when acid, and a reddish 
shade when alkaline. In the strain of P. luteum, previously de- 
scribed (Bui. 1 18, Bur. Anim. Ind. U. S. Dept. Agr., No. ii), 
the yellow is a dominant factor during the early growth of the 
organism, giving place but partially to reddish hyphae in age. 
The whole culture gets its color from the yellow granules. 
The descriptions of Wehmer^^ indicate the production of co- 
nidia much more abundantly by his strain of this species. The 
subsequent discovery of ascospores conforming to the descrip- 
tions of P. luteum in other American strains suggested the rela- 
tionship of this whole series. The ascus-producing forms when 
brought together show a progressive loss in ascus producing 
“ Hedgcock, G. G. Missouri Bot. Garden, Rept. 17, pp. 105-107. 
1® Wehmer, C. Ber. deut. Botan. Gesellsc. 1893, p. 499. 
