264 PROCEEDINGS OF THE AMERICAN ACADEMY. 



placed in the " neutral " column without making any further attempt 

 to obtain positive results by varying the substratum. A number of the 

 cultures in this column showed, before being tested, a certain difference 

 in gross appearance from those in the other columns. This is true of 

 the cultures obtained from the flowers, roots, nuts, and dung, there listed 

 from tropical regions. With these exceptions the majority of the cult- 

 ures are located in one or other of the sexual columns. Since no critical 

 examination of these forms has been made, the possibility that more 

 than one species is represented among them should not be overlooked. 

 Experiments to determine the actual condition in these neutral strains 

 have not as yet been made. 



A few of the (+) and (— ) strains constantly form perfect zygospores 

 with the corresponding test strain, but in very small amounts. The strain 

 sent by Professor Cavara from Sicily produces with the (+) strain a dis- 

 tinct line of contact wherein the zygophoric hyphae, young sporangia, 

 and progametes show the characteristic yellow coloration, yet the process 

 of conjugation as in the hybridization contrasts does not go further than 

 the formation of gametes. It is possible that in the wholly neutral strains 

 a similar reduction of the (+) and (— ) quality has extended still further 

 to the point of extinction, but it is not certain that their apparent neutrality 

 represents a complete loss of all sexual character. The sexual nature 

 may still remain, and the strains be (+) and (— ), although for some 

 reason unable to respond to a sexual stimulus. 



The table is not yet sufficiently complete to enable one to determine 

 the relative distribution in nature of the (+) and (— ) strains, but enough 

 data are furnished to show that both are widely distributed. It is hoped 

 that a further accumulation of facts will throw more light on the occur- 

 rence of these strains in nature. 



The following persons have kindly sent, for use in compiling the table, 

 material from the places indicated, and to them the thanks of the writer 

 are due : Miss T. L. Blakeslee, Delaware, Ohio ; Prof. O. Brefeld and 

 Dr. R. Falck, Breslau, Germany ; Mr. F. I. Brown and Miss L. G. 

 Adams, Brookline, Mass. ; Prof. E. A. Burt, Middlebury, Vt. ; Mr. G. D. 

 Bussey, Winthrop, Mass. ; Prof. 0. W. Caldwell, Charleston, 111. ; Prof. 

 D. H. Campbell, Stanford University, Cal. ; Prof F. Cavara, Catania, 

 Sicily; Prof. II. W. Conn, Middletown, Conn.; Prof. F. W. Coker, 

 Chapel Hill, N. C. ; Dr. E. B. Copeland, Manila, P. I.; Dr. G. P. 

 Clinton, New Haven, Conn.; Mr. J. W. Curd, Austin, Texas; Prof. 

 J. B. Dandeno, Lansing, Mich.; Prof. Ed. Fischer, Berne, Switzerland; 

 Prof. C. F. Hodge, Worcester, Mass. ; Mr. J. R. Johnston and Mr. 



