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A TEXTBOOK OF THEORETICAL BOTANY 



The zygospore retains its vitality for a considerable time and undoubtedly 

 will resist unfavourable conditions. Since, however, zygospore formation 

 is rare, it must not be regarded as the chief method of tiding the Fungus over 

 bad conditions, for the asexual spores appear perfectly capable of doing this. 

 When germination of the zygospore occurs the wall splits open and a single 

 hypha grows out which terminates in a sporangium. Considerable importance 

 is attached by some to this hypha, which is called a promycelial hypha, 

 and to the sporangium which it produces. However, the structure of the 

 sporangium differs in no way from the typical sporangium produced asexually, 

 and the spores produced in it give rise to fresh mycelia in due course. 



No definite information is available as to the position of meiosis, though 

 various workers have studied the problem. According to some the zygote 



Zygospore 



Promycelia 

 Hypha 



Sporangium 



(-) gamete 



.Mucor plant- 

 Fig. 239. — Life-cycle of Mucor. 



nucleus divides into four prior to germination, a condition analogous 

 with what occurs in Spirogyra. Many suggest that reduction division occurs 

 in the sporangium borne on the promycelial hypha. It is on account 

 of this latter view that the hypha produced by the zygospore assumes 

 special importance for, if reduction division occurs in the sporangium 

 it produces, this hypha must be diploid, in contrast to the rest of the 

 mycelium. Moreover, the sporangium formed on it must also be regarded 

 as distinct, since, unlike asexual sporangia, it is the seat of meiosis. In the 

 light of our present knowledge, however, we cannot say where meiosis occurs, 

 nor are we sure that there is actually any nuclear fusion in the zygospore, 

 though it is reasonable to assume that there is. If so, then at some subsequent 

 stage there must be a meiosis to bring back the nuclei to a monoploid state. 

 The life-cycle may be graphically represented by the scheme shown in 

 Fig. 239. 



