558 A MANUAL OF THE PENICILLIA 



the apical portion tapering to a long acuminate point (see fig. IIC) from 

 which the conidia are usually cut off as long cylindrical segments. 



In most forms the conidia are at first cylindrical, usually swell quickly 

 in the center, and commonly assume fusiform to elliptical shapes — in some 

 species becoming globose or nearly so. The cell wall may be smooth, or 

 roughened as a varietal or species character. 



The whole aspect of the penicillus is so characteristic that once it is well 

 understood, the large majority of the members of the group can be allo- 

 cated to it at once from examination under the lower objectives of the 

 compound microscope. 



There is considerable evidence that species with symmetrically bi- 

 verticillate penicilli and typically lanceolate or acuminate sterigmata 

 constitute a natural and homogeneous group. Nearly all of the strains 

 encountered produce yellow to orange or reddish colors in the aerial vegeta- 

 tive mycelium, and yellow through orange to deep red in the substratum. 

 These colors, and their transformations within the particular culture, may 

 develop quickly or slowly, and are usually intensified upon some media 

 and more or less suppressed on others. In culture media containing fer- 

 mentable sugars in the presence of inorganic nitrogen, peptone, or steep 

 liquor most of these species quickly produce a pronoiuiced and often char- 

 acteristic coloration. Thom (1930) reported the colors of P. dudauxi 

 Delacroix, as diffused in the substratum to be yellow in acid and red under 

 alkaline conditions and to be reversible with approximately the same rela- 

 tion to acid and alkali as phenolphthalein. The hyphae comprising the 

 aerial mycelium usually appear granular or encrusted when viewed dry 

 under low magnifications, and it is this superficial pigmented material in 

 massed hyphae which is primarily responsible for the bright yellow to 

 orange coloration of entire or limited colony areas in some species. In 

 other species the encrusted hyphae are less abundant and more diffuse, 

 often lending a pronounced yellow cast to otherwise dark green or dull 

 green conidial areas. 



Deceptive appearances may in some instances lead to an arbitrary and 

 erroneous allocation of species. Nevertheless, Penicillia can almost in- 

 variably be placed here if they produce (1) biverticillate conidial structures 

 which are usually symmetrical, (2) lanceolate or acuminate sterigmata 

 with long-tapered conidium-bearing tubes, (3) aerial hyphae more or less 

 yellow pigmented and encrusted, and (4) colony reverse in yellow, orange, 

 or red to purplish red shades. In addition to these forms, there are oc- 

 casional species which demonstrate certain of the above characteristics 

 with unmistakable clarity, yet fail to show others usually regarded as 

 equally diagnostic. For example, members of the PeniciUium herquei 

 series develop biverticillate penicilli that are essentially symmetrical and 



