Apr. 8, 1918 Relation of Soil Fungi to Potato Diseases 93 



the differences were sufficient to justify classifying them as separate 

 species. The species identified are as follows : 



Miicor sphaerosporus Hagem, isolated twice from sample 3. 



Mucor jansseni Lender, isolated three times from sample 3. 



Mucor spinescens Lender, isolated once from sample 3. 



Mticor circinelloides Van Tieghem, isolated once from sample 3. 



Miicor hotryoidcs Lender, isolated once from sample 3 



Mucor plumheus Benorden, isolated once from sample 2. 



Nine unidentified species of Mucor, one from group A, five from group 

 C, two from sample 2 , and one from sample 4. 



The species of this genus were identified by Mr. Zundel. 



PENICILLIUM 



A large number of Penicillium appeared in the soil cultures, and as 

 many of these were isolated as the time available would permit. The 

 separation of these forms into distinct strains was accomplished by Mr. 

 Zundel, who submitted them, with some others, to Dr. Charles Thom for 

 identification. With reference to these cultures, the following statement 

 was prepared by Dr. Charles Thom and Miss M. B. Church, of the Micro- 

 biological Laboratory, Bureau of Chemistry: 



The problem of nomenclature in Penicillium is complicated by the occurrence of 

 numerous strains with strictly asexual fruit production (conidia production only), 

 v>fhich have no reliable stnictural difTerences, but may show markedly different reac- 

 tions in culture. The study and comparison of such series collected by us, as well 

 as those sent to us by students in widely separated localities, have led to the con- 

 clusion advanced in the study of the Penicillium hiteum-purpurogenum series (15) and 

 in the study of Aspergillus nigcr (16) that there are whole groups of such saprophytes 

 genetically so related as to differ very little in morpholog>', but which differ quanti- 

 tatively in their activities. In culture such strains may be readily kept separate by 

 the contrast in color reactions produced in the nutrient media used, or by the shade 

 of color in the conidial area. In other words, this particular strain kept in pure cul- 

 ture imder fairly uniform conditions gives approximately the same picture in suc- 

 cessive culture over a long period of time. The chemistrj' of these differences is thus 

 far unsolved. Comparison of large numbers of forms, however, separates them into 

 series with the same range of variation in structure and reactions which appear to 

 differ only in quantity, not in kind. 



The soil cultures sent us by Mr. George L. Zimdel from Jerome, Idaho, contain some 

 interesting series, which are represented in every group of soil cultures we have re- 

 ceived. Not all of these forms are Penicillia. 



One series, No. 370, 467, 473, and 649 are cultures of Trichoderma, a genus constantly 

 occurring in soil and soil-polluted substances. No adequate study of these forms as 

 they occur in America has yet been made, although we have collected a large number 

 of them as the basis for such a study. 



No. 500, 504, 508, 515, with apparently accidentally admixtures in a few other cul- 

 tures, prove to be a coremiform Penicillium with affinities to P. expansum Link. 

 Members of this series have been examined from widely different sources. They 

 appear to be cosmopolitan and almost omnivorous. P. expansun, in one or more 

 of its forms, is the characteristic coremiform species found in the rotting of apples in 



