636 PATHOGENIC MICROORGANISMS 



rince. Most forms belonging to this division appear, grossly, as a 

 light, cotton-like fluff, spreading in a thin fur over the surface of the 

 culture medium. Examined with the low power of a microscope, there 

 may be seen a complicated network of fine mycelial threads, which show 

 no septa and from which delicate hyphal branches arise. In the forma- 

 tion of the asexual spore organs near the tip of each hypha a septum 

 appears. The tip of the hypha then gradually enlarges and forms a 

 spherical capsule which is known as the sporangium. The unswollen 



Fig. 145. — Mucoh mucedo. Single-celled mycelium with three hyphae and 

 one developed sporangium. (After Kny, from Tavel.) 



portion of the hypha which projects into the sporangium is spoken of 

 as the columella. Within the sporangium, a large number of small, 

 round spores are formed. When these are ripe, the wall of the spor- 

 angium bursts and the spores escape. Upon suitable media, then, new 

 mycelia develop from these spores. The sexual reproduction, which oc- 

 curs in this group, takes place in the following way: From two hyphae, 

 placed in close apposition, lateral branches grow toward each other. 

 These are spoken of as gametophores. The tips of the gametophores 

 soon come in contact and,, for a time, their protoplasm freely inter- 

 communicates. Septa are then formed which cut off from the original 

 hyphffi a central cell, the zygospore. This zygospore gradually enlarges 



