120 THE PHYCOMYCETES 



like structure. Each sporangium is multinucleate and comes to 

 contain uni- or multinucleate spores arranged in a lineal series 

 in the long axis of the sporangium. In Blakeslea trispora similar 

 development takes place, except that the sterigmate sporangia are 

 elongate spherical, and the content normally cleaves into three 

 spores. In rare cases a single spore is formed in each sporangium. 

 In Chaetocladiiim jonesii and C. hrefeldii the sporangia are re- 

 duced to the extent of containing a single spore. In the several 

 species of Mortierella and Haplosporangium the reduced 

 sporangia (sporangioles) contain 2 to 4 spores, H. bisporale con- 

 taining 2, typically. In Mycotypha microspora [Fenner (1932)] 

 the tip of the sporangiophore swells into a head, having the ap- 

 pearance of the fructification of a diminutive cattail, sterigmata 

 are formed in a spiral arrangement over its surface, and one- 

 spored sporangia are abstricted singly from the tips of each of 

 the sterigmata. 



The occurrence of many-spored, few-spored, and one-spored 

 sporangia among Mucorales is interpreted by some workers as 

 indicating progressive transformation of a sporangium into a 

 conidium. This interpretation requires that the spore wall in 

 one-spored sporangia either be not formed at all or else be com- 

 pletely fused with the sporangial wall. If the spore develops its 

 own wall and the sporangium wall is separate, even though the 

 two are closely applied, a one-spored sporangium may not prop- 

 erly be regarded as a conidium. Moreover on germination, 

 whether both membranes are extended to become the wall of the 

 germ-tube or the spore membrane alone becomes the wall should 

 be the critical feature. Apparently most mycologists seem in- 

 clined to interpret one-celled sporangia as being sporangia and 

 not conidia. 



Sexual reproduction. Sexual reproduction in the Mucorales 

 is effected by the conjugation of two morphologically similar 

 gametes. In this process a pair of lateral branches arises from 

 adjoining hyphae. These branches come into contact, swell, and 

 constitute the progametangia. Each progametangium delimits a 

 terminal cell, the gametangium. Then by fusion of the contents 

 of both gametangia the zygote is formed. A thickened, several- 

 layered wall is provided for the zygote by modification of the 

 membranes of the gametangia. 



