EUASCOMYCETES 179 



masses which give the hyphal mats their characteristic tint. This tint, 

 however, as well as the size of the conidia, varies considerably according 

 to the nourishment, temperature and physical character of the substrate. 

 Thus P. candidum forms on paper and on acid substrates a white strain 

 with white conidia just as almost all Penicilia form a white or light red 

 color on paper. If the same species grows on alkaline or protein sub- 

 strates, the mycelium is dark, almost black and forms no perithecia. On 

 carbohydrate substrates, it forms, if we may anticipate our discussion, 

 carbonaceous perithecia which together form a hard shining mass. When 

 the perithecia are emptied, the ascospores give these carbonaceous masses 

 a mealy, flabby, lustreless appearance and a coffee-brown color. That 

 variations of this sort, especially if they are caused by the presence of 

 toxic agents or experimental interference, can remain constant through 

 a long series of generations has been shown by Haenicke (1916) and 

 others. At germination, the conidia swell to three times their original 

 size and put forth several germ tubes which develop multi septate, and 

 branched mycelium. An exception to all these forms is Penicilliopsis 

 brasiliensis in which on the same conidiophores there are formed ellipsoid 

 smooth and spherical verrucose conidia (Fig. Ill, 4). The physiological 

 nutritive conditions and biological significance of this dimorphism is still 

 unknown. 



As the imperfect forms of the Aspergillaceae are the forms ordinarily 

 seen and since the physiological nutritive characters of the mycelium 

 offer very important diagnostic characters in their relation to citric acid, 

 tannins and arsenic compounds, they have been repeatedly monographed 

 (Wehmer, 1901; Westling, 1911; Sopp, 1912; Thorn and Church, 

 1921, 1926; Biourge, 1923). As has been already mentioned, many 

 forms are considerably modified by the substrate and a single description 

 to enable later identification is often almost impossible; thus in forms 

 described as Penicillium glaucum and P. crustaceum, extensive physiolog- 

 ical investigations do not determine what the various authors really 

 had in hand. 



The perithecia correspond with the perithecia of other Aspergillaceae. 

 They are generally formed on the mycelial mats, with rapid transpiration, 

 and begin to appear about 1 to 2 weeks after the inoculation of the cul- 

 tures. The laws governing their appearance are still unknown. Brefeld 

 (1874) assumes for Penicillium "crustaceum" an absence of oxygen as a 

 fundamental condition; Bezsonov (1919) shows for P. "crustaceum," 

 Aspergillus Oryzae and A. Wentii that a high sucrose content favors 

 their formation. 



With the exception of Penicilliopsis, in all species so far studied, their 

 formation is preceded by the formation of sexual organs. The process 

 taking place may be briefly discussed in five groups. In the first group, 

 as in Penicillium "crustaceum" (Brefeld, 1874) and occasionally also 



