ORDER MUCORALES 167 



bean-shaped, while they are mostly ellipsoid and more numerous and on 

 the whole smaller in the terminal sporangium. The gametangia are very 

 unequal in size. The genus Chaetodadium is parasitic upon other Muco- 

 rales. It shows close relationship to Thamnidium both in its sexual repro- 

 duction, which resembles that of Mucor, and in the production of numer- 

 ous sporangioles on forking branches some of which terminate in sterile 

 spines. The two genera differ in the complete absence of typical sporangia 

 in Chaetodadium as well as in the fact that the sporangioles are mono- 

 sporous and indehiscent, and hence are called conidia by many authors. 

 Other genera are recognized by some students of the group. (Fig. 53C-K.) 

 Family Choanephoraceae. The large sporangia are produced in 

 two genera and possess a columella and resemble those of Thamnidium. 

 The sporangioles instead of arising singly at the tips of forked branches 

 are found crowded on the surface of the swollen apical portion of a large 

 sporangiophore or of its branches. They are monosporous and indehiscent 

 in three genera and several spored and dehiscent in one genus, Blakeslea. 

 Most of the species are parasitic or saprophytic on flowers or other vege- 

 table matter. The proportion of sporangia to sporangiole-bearing heads 

 in Blakeslea has been shown by Goldring (1936) to depend considerably 

 upon the amount of food present in the medium. Choanephora produces 

 sporangia and indehiscent monosporous sporangioles, while Cunning- 

 hamella produces only the latter. Gaumann interprets the swollen apex 

 of the sporangiophore of the latter as a homologue of the sporangium and 

 the sporangioles clustered on its outer surface as in reality spores which 

 have been, as it were, pushed out so as to become external instead of 

 being produced internally. This view is not at all in accord with that 

 of the author, who considers the sporangioles to be homologous to those 

 of Thamnidium, i.e., reduced lateral sporangia. Possibly related to Cun- 

 ninghamella is the genus Mycotypha, described by Miss Fenner (1932). 

 The mycelium is like that of most Mucorales, coenocytic and much 

 branched and only occasionally septate. The sporangioles are reduced to 

 minute "conidia" closely covering the sides and apex of a cylindrical or 

 clavate enlargement of the upper portion of the eventually septate 

 sporangiophore. The resemblance of the head of sporangioles to the flower- 

 ing head of Typha suggested the name given to the organism. So far the 

 formation of zygospores has not been observed in Mycotypha. In 

 Choanephora and Blakeslea zygospore formation is much like that in 

 Piloholus but in Cunninghamella it resembles that of Mucor. The genus 

 Sigmoideomyces probably belongs to this family. Its heads of spores 

 (sporangioles) are borne laterally on branched septate sporangiophores 

 whose branches are curved more or less like the letter S. Sexual 

 reproduction is unknown. Possibly Thamnocephalis also is related. (Fig. 

 54.) 



