222 PROCEEDINGS OF THE AMERICAN ACADEMY. 



species when a second culture similar in all respects to the first produces 

 them in abundance. A failure to obtain zygospores by making a gross 

 transfer of sporangia from a zygosporic culture may be due to the fact 

 that one of the strains has short sporangiophores, and thus may escape 

 below the taller growth of the other. To say that all species are hetero- 

 thallic in which the production of zygospores from spore sowings has not 

 been a constant phenomenon under similar culture conditions, would at 

 present be too sweeping a statement, yet such is undoubtedly the condi- 

 tion in the forms with which the writer is familiar. From actual knowl- 

 edge and from indirect evidence, the heterothallic condition seems to be 

 the more common among the Mucorineae, and if we are to lay the 

 burden of proof on either side we should be led to consider a species 

 heterothallic until it has been proved otherwise. 



Of the 66 forms cited below, the occurrence of zygospores or azygo- 

 spores in 51 cases has been reported but once, and in the remaining 

 species, a list of which is appended, the number following each form 

 indicates by how many authors the zygospores have been found and re- 

 ported, — Mucor Mucedo, 6; M. racemosxs, 4; M. fragilis, 2; M. erec- 

 iits, 3 ; Zygo7'hynchus Moelleri, 2 ; Phycomyces nitens, 2 ; Spinellusfusiger, 

 many ; Sporodina grandis, many ; Rhizopns nigricans, 5 ; Absidia cae- 

 rulea, 2 ; Pilaira anomala, 2 ; Chaetockidium Brefeldii, 4 ; Piptocephalis 

 Freseniana, 2 ; Syncepkalis nodosa, 3 ; Syncephalis Cornu, 4. 



Since the purpose of the present paper is in no sense systematic, no 

 attempt is made to include a special study of the nomenclature and sys- 

 tematic position of the species cited. In so far as possible A. Fischer's 

 ('92) admirable and familiar classification of the group has been followed. 



Mucor Mucedo Linne. 



" Following a sowing of Helicostylum on dung, zygospores appeared 

 in abundance after twelve days in the recesses where the brownish my- 

 celium was protected against access of air and light." This note of van 

 Tieghem's ('72, p. 1000) is the first reported occurrence of the zygo- 

 spores of M. Mucedo. 



Brefeld ('72) states that zygospores never appeared on his slide cul- 

 tures, though their occurrence was not infre(iuent in spontaneous cultures 

 of horse dung where he first found them. In speaking of the zygophores 

 he says : " It is fairly certain, however, that they do not arise from two 

 branches of the same hypha as in Sporodinia. since in the youngest con- 

 dition observed the copulating hyphae could be followed for a considera- 

 ble distance." 



