10 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



collecting these forms, many of them have been isolated in this 

 laboratory from dairy products and from fruits, or collected in the 

 field by the writer. One series of forms was purchased from Krai, of 

 Prague. Several species have been contributed by or verified by 

 those who described them — two by Dr. G. Bainier, two by Dr. C. 

 Welimer, one by Dr. G. Delacroix, and one by Dr. G. G. Hedgcock. 

 Many correspondents have sent cultures for examination or study. 



THE BASIS FOR SPECIFIC CHARACTERIZATION. 



The available sources of identification of these species will be 

 discussed first. By the kindness of Professor Thaxter the exsiccati 

 of the genus in the herbarium of Harvard University were examined. 

 Cultures of certain species were tried but no living spores were 

 found. No specimen was found in such condition as to be used to 

 identify material by comparison. Similar courtesy was extended 

 for the examination of specimens in the herbarium of Kew Gardens 

 and at the University of Berlin. In no case was material found by 

 which cultural material could be identified or identification verified 

 by comparison. The plant bodies are too evanescent to retain the 

 criteria necessary for identification for any great length of time, as 

 ordinarily preserved. In most cases after a few years of handling 

 the specimens were found reduced to powder. Welimer 33 has noted 

 for certain species of this genus that the conidia do not retain their 

 power to germinate beyond a very few years. Specimens as formerly 

 prepared therefore become useless for the identification of species 

 by the method of types. The method described by Hedgcock 9 for 

 preserving specimens has thus far been applied only to one species 

 of Penidllium and entirely too recently to test its permanent value. 

 Aside, therefore, from certain species which will be discussed later, 

 it has been impossible to determine material belonging to this genus 

 from herbarium specimens. 



. There remain two methods of identification: (1) The identification 

 of material or cultures by the authors of descriptions; (2) identifica- 

 tion by critical study of the descriptions and illustrations published. 



Regarding the first method, fortunately some of the more recent 

 authors have either preserved their organisms in culture, as is done 

 at the Ecole de Pharmacie in Paris with the cultures of Bainier, or 

 placed them in one other of the distributing laboratories where 

 such organisms are maintained in continuous culture. But the earlier 

 authors are dead and have left only their published descriptions and 

 figures as a means of determining what organisms they studied. 



Turning to the critical comparison of material with published 

 descriptions, we find many difficulties. These descriptions give in 

 meager outline observations of mold masses showing penicillate coni- 

 dial fructifications, as found in nature upon substrata more or less 



