50 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



politan species associated with the decay of many kinds of food stored 

 in wet condition or in humid situations. Typical clusters of spor- 

 angiophores are borne on stolons or runners, which are hyphae extending 

 radially from the center of the colony and fastened to the substratum 

 or to the support at intervals by root-like outgrowths. Abundant 

 growth of this species is found only under very moist conditions or 

 in substrata with high water content. Rhizopus is a very common 

 contamination in laboratory cultures. 



Many species and races of Rhizopus have been described. These 

 have been studied especially in connection with the fermentation 

 industries of Japan and China. Rice, wheat, and soy-beans in various 

 mixtures pass through an initial process of " Koji" preparation in which 

 raw or cooked materials are exposed to the air for several days. These 

 processes offer ideal conditions for the entrance of the mucors as 

 contaminations among the organisms desired. 



There are many common species of the genus Mucor, very few of 

 which are identifiable without critical study. The specific names as 

 commonly cited often designate groups of species or varieties rather 

 than sharply marked forms. Certain of these may be briefly considered. 



Mucor mucedo L. is a common form upon dung, characterized by 

 heads (sporangia) upon long sporangiophores,* at first yellow then 

 becoming dark brown or black and studded upon the surface with 

 needles of lime. 



Mucor racemosus, Fresenius, is characterized by the production of 

 chlamydospores or cysts in the mycelium within the substratum, as 

 elliptical thick-walled cells. The sporangiophores typically branch to 

 make racemes of sporangia. The racemose mucors are active agents in 

 changing starch to sugar and in the production of traces at least of 

 alcohol from sugars. 



Mucor rouxii (Calm.), Wehmer, (syn. Amylomyces rouxii) is the 

 most important of a series of forms with sporangiophores branching 

 sympodially which are active in changing starch to sugar and in produc- 

 ing traces at least of alcohol. The mycelium of Mucor rouxii develops 

 in fluid cultures as yeast-like cells and groups of cells. The typical 



* The term sporangiophore is composed of the word sporangium combined with the suffix 

 phore, meaning bearer. In sympodial branching the first fruit is on the tip of the original hypha, 

 the first branch arises below this fruit and is terminated by the second fruit. Each successive 

 branch and fruit originates in similar manner. 



