THE GENUS PENICILLIUM. 331 



to brownish, though yellowish, white, and brown species are 

 known) ; the branching of the conidiophores and the size and 

 shape of the conidia, together with other, slighter characteristics, 

 especially those of a physiological nature, such as pigmentation, 

 energy of growth, gelatin liquefaction, acid production, food-stuff" 

 requirements in respect of the various sources of carbon, nitrogen, 

 &c. Except in the case of the collective species "P. glaucum" little 

 was known until recently of their requirements as to temperature. 

 No mention has yet been made of species that thrive at blood-heat, 

 and the maximum seems to be lower than 37 0. STOLL (I.) quite re- 

 cently published certain observations in this connection with regard 

 to six species more closely examined, morphologically and in cul- 

 tures, by him, from which it appears that only P. purpurogenum 

 and P. rubrum thrive best at higher temperatures (30 C. in the one 

 case and 3o-35 C. in the other), the optimum temperature for the 

 remainder being below 30 C., viz., P. italicum, 25 C. ; P. oliva- 

 ceum, 23-25 C. ; " P. glaucum" and P. brevicaule, 2O-23 C. 

 The colour of old herbages, especially when grown under uncon- 

 trollable conditions, is, of course, useless as a means of differentia- 

 tion, and probably a number of grey, brown, and dark-coloured 

 species mentioned in the older literature owe their existence to 

 these fictitious differences. As in the case of Aspergillus, the 

 colour is frequently dependent on the character of the substratum, 

 an alkaline reaction of the latter appearing to cause the green to 

 turn greyish brown. 



In the present unsatisfactory state of knowledge on the Penicil- 

 lium group, the number of species taking part in the ripening of 

 cheese, and the production of mould and decay in fruit, is about 

 six or seven, though the list will probably be increased to some 

 extent in time. A noteworthy fact, in comparison with Asper- 

 gittus, is the absence of any species pathogenic to animals, or of 

 technical value outside Europe ; at least, the few that are said to 

 be pathogenic, inhabiting mucous membrane and animal substrata, 

 have a very doubtful existence as distinct species (P. quadrifidum^ 

 Salisbury ; P. pruriosum, Salisb., &c.), and there is a wide field 

 open for subsequent research. A so-called P. minimum, found by 

 SIEBENMANN (I.), in the ear of a patient, needs further explana- 

 tion. F. DIERKX (I.) in a recent preliminary communication, 

 gave no less than twenty-two new species (almost completely 

 ignoring those already known), but gave no illustrations or suffi- 

 cient description of them. Moreover, the habitat of the newly 

 found "species" being unstated, it is difficult to accept them as 

 genuine, and the matter is not advanced at all by this communi- 

 cation, despite the accuracy of the principles laid down by that 

 author, who lays stress, inter alia, on the necessity for culture 

 experiments for describing a species. A publication by STOLL (I.), 

 shortly before the completion of the present manuscript, adds to 

 our knowledge of the Penicillium group, by detailing a series of 

 observations on comparative cultures of several species. Further 



