224 REPRODUCTION OF BLACK MOULDS 



The ability of these spores, or sporangia, to produce zoospores is 

 doubtless the survival of a trait inherited from their algal an- 

 cestors. 



80. Order c. Mucorales or Black Moulds. — These are among 

 the most common of the fungi and they are almost sure to appear 

 upon any cooked food or decaying matter that is exposed to the 

 air even for a very short time (Fig. 134). The mycelium has 

 practically the same structure as noted in the preceding groups, 

 but the black moulds have lost all motile reproductive bodies and 

 their relationship to any group of the algae is not known. Some 

 of the hyphae of the mycelium creep over the food supply and 

 send into it short branches which serve as organs of absorption 

 while other rather thicker hyphae grow away from the mycelium 

 and reach up into the air (Fig. 134). The tips of thesfe erect 



Fig. 134. Habit of growth of the black mould, Rhizopus: s, sporangia; 

 r, absorbing branches of the mycelium. \^ 



hyphae enlarge owing to the accumulation of protoplasm and 

 numerous nuclei in them, and finally become spherical, forming 

 the sporangia. The contents of the young sporangia differentiate 

 into a denser peripheral portion containing the bulk of the nuclei 

 and a more watery central and basal region. A layer of large, 

 round vacuoles now appears between these two regions and, 

 owing to the flattening out and fusion of these vacuoles, a cleft 

 is formed that ultimately separates the peripheral from the central 

 protoplasm. Next furrows advancing inward from the sporangial 

 wall and outward from the cleft divide the peripheral protoplasm 

 into numerous small portions, each part containing several nuclei, 

 hese bodies round off, secrete a rather thick smoky black wall 



