220 PROCEEDINGS OF THE AMERICAN ACADEMY. 



pass into the germ tube. The fusion in the formation of the '' Spheres 

 embryonuaires " is looked upon as the only sexual part of the process. 

 On this basis the azygospores are to be considered equally sexual, since 

 they diflfer from the zygospores only in containing a single " Sphere 

 embryonuaire." These observations of Leger have not been confirmed 

 by Istvanfii ('95) nor by Gruber ('01), who worked carefully on the 

 zygospores of the same form, Sporodinia grandis, and Dangeard ("96, 

 p. 255), in collaboration with whom Leger began his investigation, disputes 

 his pupil's later results. The writer also, from an investigation as yet 

 incompleted, of sections of the zygospores of a number of different 

 species, is satisfied that they contain no structures corresponding to 

 " Spheres embryonuaires." 



Although the exact nuclear history in the process of conjugation is a 

 matter of great interest, a knowledge of it is not necessary in order to 

 establish the sexuality of the act. Nuclear fusion is considered to be the 

 criterion of a sexual process, yet, as is seen from the nuclear fusion in 

 the ascus and basidiospores, one must have recourse in addition to physio- 

 logical considerations for an interpretation of the sexuality involved. 

 The results set forth in the present paper show beyond question that 

 sexuality is present in at least a very large percentage of the Mucorineae, 

 and cytological investigation can merely extend our knowledge of the 

 details of a process, the true character of which seems obvious without 

 its aid. It will be of especial interest to determine the cytological con- 

 ditions in connection with the segregation of the sexes occurring in the 

 formation of zygospores or later, but no systematic experiments with 

 the germination of zygospores have been made during the present inves- 

 tigation. The writer hopes, however, in the near future to be able to 

 present more satisfactory data on the subject. 



CITATION OF SPECIES FROM WHICH ZYGOSPORES HAVE 

 BEEN REPORTED. 



In the preparation of the ensuing references, recourse has been had to 

 Just's Jahresbericht for the years 1876 to 1902 inclusive, and to the Bo- 

 tanische Centralblatt for 1903 and for the present year up to May 1. 

 For some of the later species Saccardo's Sylloge has been trusted to 

 mention the occurrence of zygospores when they have been reported in 

 the original description, but the compilation of Berlese and de Toni ("88) 

 in Volume VII is of little value in this respect, and fails to mention even 

 the zygospores of Rhizopus nigricans. Although the writer has eudeav- 



