58 A MANUAL OF THE PENICILLIA 



different species included. The perithecia in this series merge imper- 

 ceptibly into ascosporic structures of the type usually included in the genus 

 Gymnoasciis. Derx (1925-1926) reported a strain of P. luteiim to be het- 

 erothallic, but this has not been confirmed by subsequent investigators. 

 Emmons in 1935 tested each of the ascosporic species studied by him and 

 reported all of them to be homothallic. During the past few years a con- 

 siderable number of ascosporic Penicillia have been described and a 

 thorough study of these forms, extending the excellent work of Emmons, 

 should be undertaken. 



The discovery of perithecia in any culture greatly facilitates the identi- 

 fication of that form. We cannot, however, place primary emphasis upon 

 the presence or absence of such structures in the taxonomy of the genus 

 Penicilliiim. The student of these molds still requires a means of identi- 

 fying conidial forms which continue to constitute 90 per cent or more 

 of the organisms which appear in his cultures. 



CYTOLOGY 



Gueguen in 1898-1899 reported work upon the cytology of Penicillium 

 glaucum. Cultures upon moist bread were taken as normal. Best results 

 were obtained without fixation . The conidial wall was reported to be com- 

 paratively thick, representing one-fifth of the total diameter, and showed 

 in optical section alternate areas thin and re-inforced, hence staining dif- 

 ferently. The old spore wall was seen and figured on the remains of the 

 swollen cell in contrast to the thin wall of the growing hypha in the ger- 

 minating conidium. He depended upon intravitum staining with gentian 

 violet or dahlia in very dilute solutions. \^egetative cells were reported to 

 be multinucleate, and the cells of the conidiophore were not different in 

 structure from those of the vegetative hyphae. The branches and metulae 

 were also multinucleate. He figured the young sterigma as at first multi- 

 nucleate, the actual number being variable, then reduced (fusion is sug- 

 gested) to two, one of them centrally located, the other at the point of 

 conidium formation. Although two nuclei are figured in the sterigma 

 and the conidium in the process of separation, he reported only one nucleus 

 in the conidium when separation was complete. His inference was that 

 before the wall was laid down, one of the two nuclei in the developing coni- 

 dium migrated back to the apical position in the sterigma to become the 

 nucleus of the next conidium and to be replaced at the apex of the sterigma 

 by another produced by division of the central nucleus. Multinucleate 

 conditions were resumed in the process of germination. 



More recently, Baker (1944a and 1944b), studying the cytology of 

 Penicillium notatum, reported the conidia to be usually uninucleate or 

 occasionally binucleate. A single conidium can develop into a typical 



