294 PROCEEDINGS OP THE AMERICAN ACADEMY. 



alike for the purposes of the present paper to l)e treated as one, and 

 though more cultures have beeu made with Mucor i the facts here 

 presented will apply to them ajl. Mucors i and ii are alike as far as 

 their method of conjugation is concerned. They apparently disagree 

 slightly, however, in their action in cultures and in their relations to 

 temperature; and in cell cultures Mucor i, moreover, produces chlamydo- 

 spores which bud in a characteristic Oedocephalum-like manner not 

 possessed by Mucor ii, but it is uncertain whether the slight differences 

 which may exist are sutlicieut to separate these forms as distinct 

 sijecies. 



The process of conjugation is similar to that determined in some detail 

 in Mucor Mucedo. That there is a mutual attraction between the zygo- 

 phoric hyphae is probable, and progametes which here as in all other 

 cases always result from hyphal contacts, are frequently produced be- 

 tween the terminal portions of hyphae of such considerable length as to 

 suggest that contact was brought about by the mutual orientation of the 

 hyphae affected. In a few instances also in cell cultures hyphae have 

 been observed growing toward each other and producing progametes at 

 their point of contact. Not enough observations have been made, how- 

 ever, to demonstrate that this meeting may not be accidental. Attempts 

 to follow the zygophoric hyphae is an uncertain task, since in cell cul- 

 tures sporaugial formation predominates and the production of zygo- 

 spores cannot be limited to a single line, as can conveniently be done in 

 the heterothallic forms. Moreover the zygophoric hyphae are not always 

 readily distinguishable from the sporangiophores, and it has thus several 

 times happened, during the course of an observation, that all the hyphae 

 whose positions had been mapped and followed by the aid of a camera 

 lucida have later been found to produce only sporangia. It can, how- 

 ever, be stated from observation that the contact of zygophoric hyphae is 

 the stimulus for the outgrowth from them of the progametes, and that 

 the latter never arise independently. 



That the thallus of this plant is in fact bisexual has been shown by its 

 resijonse to both the sexual strains of a heterothallic species in the pro- 

 cess of "hybridization" subsequently described (cf. p. 311 and Plate IV, 

 Figure 56). No experiments have as yet been made, however, which 

 will enable one to determine where the se^rregatiou of the sexes occurs 

 before the formation of gametes. It is possible that any zygophoric 

 hyphae may produce progametes when brought into contact with any 

 other, and the segregation might then occur at the moment wlien the 

 gametes were cut off. That such a process may occur is suggested by 



