RLAKESLEE. — SEXUAL REPRODUCTION IN THE MUCORINEAE. 299 



the slender zygophoric filament. It sometimes happens that a short 

 stalk remains after the smaller gamete is distinguished (Figure 4), and 

 although it fails to enlarge and in the mature condition is hardly uotice- 

 able, its origin warrants the use of the term suspensor. 



In some old cultures, cells have not infrequently been found in dif- 

 ferent stages of development, ranging from a condition in which the wall 

 is only slightly discolored and papillate, to a condition with dark dis- 

 tinctly denticulate thick walls resembling, except in size, a mature zygo- 

 spore (Figure 9). They are apparently formed from the smaller 

 gamete developed from the less vigorous zygojihoric filament, and on 

 this supposition may be called azygospores. Though it is possible that 

 azygospores are formed from the more vigorous zygophoric branches, 

 such a condition has not been observed. It has not been possible to 

 follow in detail their production, and to determine the immediate stimulus 

 to their formation. The only explanation known for the origin of pro- 

 gametes is contact between the opposing zygophoric hyphae, and although 

 no cases have been observed in which a contact could be considered 

 responsible for the origin of the cells in question, their position on the 

 filament and their general appearance suggests that they have been cut 

 off from single progametes. 



Although the species considered has been under cultivation for about 

 ten years, and continued in pure cultures through many generations of 

 non-sexual spores, no substratum nor external condition has been found 

 which would prevent the formation of zygospores, notwithstanding the 

 fact that all nutrients were tried for its cultivation which were used in 

 the tests with Mucor i and ii (p. 293) and Rhizopus (p. 248). The 

 production of sporangia has been always less than that of zygospores, 

 and it is often difficult to obtain preparations showing the former in any 

 abundance. 



In fiuid nutrients like dilute decoction of prune, there is no fermenta- 

 tion nor production of yeast forms, and fructification only occurs when 

 the mycelium reaches the surface, where it gives rise to a scanty growth 

 of sporangia and zygospores. Nutrients of high concentration have 

 not been used, but on such dilute nutrients as can be obtained from 

 tap water in pure agar, or even from tap water alone on a sponge, 

 zygospores and sporangia are formed together, although their production 

 is feeble. 



In the dryest atmospheres obtained, namely, in a sealed vessel with 

 calcium chloride, zygospores are produced in abundance, as is also the 

 case when the surrounding air is rendered nearly saturated by layers of 



