PEKICILLIUM 



105 



slight swelling of the tip of the conidiophore. But Thom places them 

 with the Penicillia, because numerous other typically penicillate 

 forms have been found subsequently, and because the foot-cell char- 

 acteristic of the Aspergilli is lacking. 



Species of the Citromyces group were investigated at one time as 

 a possible means of producing citric acid commercially, but without 

 much success. 



Biverticillata-symmetrica. This section contains a fairly homoge- 

 neous group, of which P. luteum is the commonly known species.- 

 Ascospores are formed regularly by 

 some strains of P. luteum in loose 

 masses of pseudoparenchyma, not in 

 well-defined perithecia. This section 

 is also characterized by the production 

 of pigment, in the form of granules on 

 the mycelium, which varies from yellow 

 through orange to red, the color chang- 

 ing with the species, substrate, and age 

 of the culture. P. pinophilum, produc- 

 ing stains on wood, belongs in this sec- 

 tion, as does also the organism used in 

 gluconic acid production. 



Poly vert icillata-symmetrica. This is 

 a small group of four species, none 

 of which is of practical importance. 



Asymmetrica. The great majority of the Penicillia fall in the 

 asymmetric group, including most of those of. any economic impor- 

 tance. This section is divided into several subsections. 



Velutina. The colonies have a velvety appearance. P. digitatum 

 and P. expansum are important species. 



Brevi-compacta. Colonies are partly velvety, partly woolly in 

 texture, the penicillus biverticillate and showing characteristically a 

 short compact base with divergent sterigmata and conidial chains. 

 P. stolonijerum, growing on mushrooms and other fungi, and spread- 

 ing by means of aerial runners, belongs here. 



Lanata-typica. This is characterized by an abundance of aerial 

 mycelium which gives the colony a woolly texture. Conidia appear 

 first in the center of the colony after the felt of aerial mycelium has 

 been established. P. camemberti is an important species. 



Lanata-divaricata. Here the branches of the penicillus are widely 

 divergent and a looser type of spore head is produced than in the 

 other groups. A series of species characteristically found in soil, of 



Fig. 53. Penicillia from cheese : 



a, Penicillium roqueforti; b, P. 



camemberti. 



