BLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORTXEAE. 297 



no cultures have given an exclusive production of zygospores. In this 

 instance, the soft agar used and the probable fact that the mycelium 

 developed from a single spore may have especially favored zygospore- 

 formation. 



From the foregoing experiments it is evident that, in cases where the 

 vegetation is interfered with, the formation of zygospores is apparently 

 inhibited before that of the sporangia. In this connection it is interesting 

 to note that, while in one of the forms obtained from soil by Hansen 

 ('02) a similar relation existed between zygospore formation and un- 

 favorable conditions at least of temperature, in another form from the 

 same source the sporangia under similar conditions were found to be 

 inhibited before the zygospores. In conclusion it may be said, in so far 

 as concerns the three homothallic Mucors above discussed, that, in 

 general, external conditions not obviously unfavorable to the growth of 

 the fungus have no influence in determining which form of reproduction 

 will occur 



Ztgorhynchus Moelleri. 



This homothallic species, as already mentioned in the Citations in 

 Part I (p. 227), has been found a number of times, the form with which 

 the writer has experimented having been obtained at New Haven in a 

 separation culture from soil by Professor Sturgis. It is similar in its 

 mode of conjugation to Z. heterogamus, the other member of the genus 

 which Vuillemin has separated from ^Mucor on account of the constant 

 dissimilarity in the gametes. It may not be out of place in the present 

 paper to give a brief account of the process of conjugation observed by 

 the writer in Z. Moelleri.^ although in the main it will be but a repetition 

 of the detailed description already given by Vuillemin in the other 

 species. 



In Mucors i and ii, as has been seen, the zygophores generally arise 

 from comparatively distant parts of the mycelium, and although their 

 origin may be close together on the same mycelial filament, yet so far 

 as has been observed zygospores are never formed between branches 

 of a single aerial hypha. In Zygorhynchus, however, the conditions are 

 reversed, and the two zygophoric branches almost invariably not only 

 originate from a single aerial hypha, but have a definite position on the 

 filament, and conditions in which zygospores have been observed to 

 form between filaments connected with distant parts of the same my- 

 celium are comparatively rare. 



In the simpler case illustrated by the more common mode of conjuga- 



