BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 207 



PART I. 



INTRODUCTION. 



Among the INIucoriueae the usual form of reproduction is by means of 

 nonsexual spores in sporangia. Although the sexual method of repro- 

 duction by zygospores has, through the researches of individual investi- 

 gators, now been found in nearly all the genera, it is still in a majority 

 of the species entirely unknown, and our knowledge of its occurrence in 

 about four-fifths the cases rests on the unconfirmed reports of single 

 individuals. The only common species which could be depended on to 

 produce its zygospores has been Sporodinia grandis. Ever since de Bary's 

 ('64) investigation of this form and of Rhizopus nigricans ('66) the causes 

 inducing the formation of zygospores have been a subject of much 

 speculation and considerable study among mycologists. The elaborate 

 papers of Klebs ('98) and Falck ('01) have given us much conflicting 

 information on the problem in Sporodinia, but attempts to apply the 

 results of these investigations, or of the earlier researches of van Tieghera 

 and others, to the Mucorineae in general, with a view to obtaining zygo- 

 spores, have proved ineffective. Since the evidence on this subject, in a 

 form like Sporodinia for example, which has been most thoroughly exam- 

 ined, is not only conflicting, but is evidently inapplicable to a majority 

 of existing forms, it has been the aim of the present paper to consider the 

 conditions which lead to the production of zygospores in the group as a 

 whole rather than in any single species. 



In 1901, at Professor Thaxter's suggestion and under his direction, the 

 writer began the collection and preservation in pure cultures of forms 

 of the Mucorineae, but especially of the genus Mucor, having in mind, as 

 has already been mentioned, a subsequent monograph of this confused 

 genus. In the course of this preliminary work zygospores of different 

 species were several times found, but the forms differed greatly in their 

 behavior. Some of them, among which Sporodinia may be taken as a 

 type, could be readily induced to produce zygospores on a suitable sub- 

 stratum when a pure transfer was made by means of spores taken from 

 a single sporangium ; others, of which Rhizopus may be taken as a type, 

 would never form zygospores from a pure transfer, but only when a mass 

 of spores from a zygosporic culture was used for the inoculation. Of the 

 first class, all have been isolated and kept running in tube cultures with- 

 out abatement in their zygosporic activity, but with such species of the 

 second as could not be separated from the abundance of other fungi and 

 bacteria and preserved with their zygospores on the dried substratum, it 



