ORDER MUCORALES 



161 



by twos. The dormant zygospore contains only diploid nuclei which 

 undergo meiosis shortly before their germination. In Phycomyces blakes- 

 leanus Burg, and P. microsporus van Tiegh., of which at least the former 

 is heterothallic, the nuclei increase in number in the zygote and become 

 gathered in groups of several nuclei each, with a few scattered single 

 nuclei. Shortly before germination of the zygospore some of the nuclei 

 unite by twos and in the sporangium arising from it are found some 

 diploid nuclei, some haploid nuclei, the product of meiosis, and probably 



Fig. 56. Mucorales, Fam- 

 ily Kickxellaceae. (A, B) 

 Coemansia erecta Bainier. 

 (A) Vigorously growing coni- 

 diophores. (B) Sporocla- 

 dium. (C) Coemansia aci- 

 culifera Linder. Mature 

 sporocladium and a single 

 detached conidium. (Cour- 

 tesy, Linder: Farlowia, 

 l(l):49-77.) 



also some haploid nuclei which represent the scattered single nuclei 

 which never united. In the homothallic Sporodima grandis, contrary to 

 Lendner's report, there is nuclear division in the zygote but no nuclear 

 fusion and no meiosis. 



Germination generally does not occur until after a considerable time 

 has elapsed. Usually a stout upright sporangiophore is sent out after the 

 outer wall is cracked open, and numerous spores are formed in a large 

 sporangium. In the plant usually called Mucor mucedo (L.) Fres., a 

 heterothaUic species, the spores produced in this sporangium are all of 

 one sex, showing that the differentiation of the sexes must have occurred 

 in some nuclear division within the zygospore prior to its germination. 

 On the other hand in Phycomyces nitens spores of both sexes are found in 

 the sporangium produced by the germinating zygospore, as well as, 



