88 



MOLDS BELONGING TO THE PHYCOMYCETES 



M. hiemalis is very similar but the columella is typically spherical 

 (Fig. 35). It is concerned with the retting of flax, secreting an 

 enzyme which dissolves the middle lamella of the intercellular sub- 

 stance. It digests starch and gelatin and ferments dextrose but not 

 sucrose. It also is heterothallic. 



M. piriformis is recognized by its very large sporangia and pear- 

 shaped columella. It is found on spoiled fruit and is claimed to be 

 a cause of soft rot of pears. 



M. racemosiis is the most common of the Racemomucors, and 

 though of little practical importance it is of some scientific interest. 



It is remarkable because it produces an al- 

 coholic fermentation of sugars, and, when 

 it is submerged in sugar solutions, the my- 

 celium breaks up into a series of spherical 

 oidia (Kugelzellen or Kugelgemmen in Ger- 

 man literature) which may continue to grow 

 as single cells by budding, like yeasts (Fig. 

 37). The association of the yeast-like form 

 with alcoholic fermentation naturally at- 

 tracted great interest. It is curious that 

 these round oidia are formed only by Mucors 

 which also produce alcohol. Their resem- 

 blance to yeasts is only superficial, as they 

 are much larger and each cell contains 

 many nuclei. M. racemosus is easily rec- 

 ognized by the characteristic branching of the 

 sporangiophores. The sporangial wall is 

 frequently covered with tiny crystals of 

 calcium oxalate, and the columella is some- 

 what pear-shaped. Inoculation into glucose 

 broth fermentation tubes will show the pro- 

 duction of gas and yield the spherical budding 

 cells in the sediment. Perhaps the most striking character is the 

 abundant formation of the jet-black chlamydospores in the aerial 

 mycelium. M. racemosus may be distinguished from the closely 

 related M. erectus and M. fragilis by the form of the columella. The 

 latter two species also form slight amounts of alcohol from sugar and 

 give rise to budding oidia in the submerged portions. 



M. circinelloides is frequently encountered in soil cultures. It ex- 

 hibits true cymose branching (Fig. 38). Budding oidia are formed 

 in mycelium submersed in liquid media. M. plumbeus is also a 

 common soil form. It derives its name from the lead-gray color of 



Fig. 38. Mucor circi- 

 nelloides: sporangio- 

 phores showing typical 

 cymose branching. 



