MOLDS 53 



substrata. Starches and sugars appear to be especially favorable 

 components of nutrient media for members of the group. The larger 

 number of the species grows best at temperatures from 15 to 30; 

 a very few of them reach their optimum at 37, but many species are 

 entirely inhibited and some killed at blood-heat. Vegetative mycelium 

 begins to be produced at temperatures very close to freezing, but 

 colored conidia are produced slowly or not at all at low temperatures. 

 The species of Penicillium thrive through a wide range of concentration 

 of culture media, though perhaps the most characteristic growths are 

 produced in media high in water content. The common species of 

 this genus grow in all the standard bacteriological media. With few 

 exceptions the species grow well in synthetic media composed of 

 assimilable carbohydrates and inorganic salts. A few species require 

 the presence of some one of the higher nitrogenous compounds, but 

 many species refuse to produce typically colored fruit without some 

 form of starch or sugar in addition to ordinary peptone and beef- 

 extract. Very few species grow well in alkaline media, but most 

 species are tolerant of organic acids at the concentrations found in 

 fruits and vegetables. 



Some Common Species. Penicillium roqueforti, Thorn, is a green 

 form constantly found in pure culture in Roquefort cheese, frequently 

 also in ensilage. It is widely distributed and grows under many sets 

 of conditions. 



Penicillium camemberti, Thorn, is the chief organic agent in ripening 

 Camembert cheese. Cultures of this species are floccose or cottony, 

 at first white, later gray-green. 



Penicillium expansum, Link, is a green form, always obtainable from 

 apples decaying in storage, upon which it frequently produces large 

 coremia or stalks bearing conidia in masses sometimes several millimeters 

 in diameter. It is one of the most abundant species of the genus, 

 widely distributed in different countries. In cultures, colonies produce 

 a characteristic odor, suggestive of its common habitat, decaying apples. 



Penicillium brevicaule, Saccardo, (Scopulariopsis repens, Bainier) 

 is a form with rough or spiny brown spores which has been used phy- 

 siologically to detect the presence of arsenic by its ability to set free 

 arsine from such substrata. A whole series of forms has since been 

 found to possess this character correlated with characteristic spore 

 formation. These species or races are common in the soil both in 



