136 
Mycologia 
nical characterization which will surely separate them is exceed- 
ingly difficult. The common morphological characters have, 
therefore, been brought together to define the section Verticillatae 
of the whole group of penicillate organisms in the sense of 
Wehmer. These characters follow : 
IMorphological characters of Section Verticillatae 
Conidiophores vary greatly in length. Each conidiophore typ- 
ically produces a crown or verticel of metulae,® or fertile branches. 
From this arrangement Wehmer derives the name Verticillatae. 
The metulae are few to many in the verticel ; the number differs 
in the different members of the series. They are usually closely 
clustered. Careful search in nearly every strain shows an occa- 
sional conidial fructification in which a secondary verticel is borne 
either upon the main conidiophore prolonged through the center 
of the primary verticel or upon some one of the metulae of the 
primary series. Both conditions are found, but only in small 
numbers under the usual conditions of culture. 
This section includes many species, some of which form series 
in which further relationship is suggested. Others diverge widely. 
One such series of forms has been collected and may be desig- 
nated the luteum-purpurogenum series from the well known 
forms which stand at the extremes. 
The luteum-purpurogenum series 
At one end of this series stands a strain of P. luteiim^^ Zukal 
which produces ascospores freely in all the media used and co- 
nidia very sparingly. In the actively growing culture the domi- 
nant shades of color are yellow with tardy appearance of red. 
At the other end stands P. purpurogcnum Stoll,^^ which produces 
only conidia, in which yellow shows transiently, while red colors 
in mycelium and substratum are abundant. 
9 Westling, R. Arkiv. for Botanik. Bd. ii, No. i, p. 44, in Ueber die grunen 
spezies der Gattung Penicillium. 
“Described as P. luteum in Bui. 118, B. A. I. U. S. Dept. Agr. The cul- 
ture was cultivated by Prof. R. Thaxter in 1905. 
“ Stoll, O. Beitrage zur Morphologischen and biologischen Characteristik 
von Penicillium, Inang. Dissert. Stuttgart 1903-4. 
