98 MEDICAL MYCOLOGY 



continuing growth and reproduction saprophytically on dead insects. Only 

 the Mucoraceae have been found parasitic on mammals. Basidioholus hominis 

 has recently been reported but has been so poorly described that its relation- 

 ships are still obscure. 



Mucoraceae. — This family is commonly saprophytic on plant or animal 

 remains, more rarely parasitic on other Mucoraceae, on higher plants, or on 

 animals. They play a large part in the decay of organic substances and a fow 

 species have some economic importance because of fermentations, such as 

 alcoholic fermentation by Mucor javanicns or starch hydrolysis by Rhizopns 

 Oryzae (Wehmer 1907). 



Except in Haplos%)orangium, where the hyphae are early divided into 

 multinucleate segments by septa, the thallus consists of branched coenocytic 

 hyphae without septa ; in senescence or in the development of reproductive 

 structures, septa are formed irregularly to cut off older vacuolate sections 

 from the younger portions. Furthermore, the hyphae of some genera, in high 

 concentrations of sugars and anaerobic conditions, break up into oidia which may 

 develop further by sprouting ; this sprout mycelium may ferment sugars very 

 much as the true yeasts. (Fig. 2.) In Mortierella and Syncephalis, hyphal 

 branches may fuse where they come in contact with each other, so that the 

 mycelium becomes an anastomosing network. In general, heterothallic species 

 have no definite sexual dimorphism, the strains usually differing slightly in 

 physiologic characters or the positive (female) strain being better developed. 



Only a few details are known concerning the internal structure of the 

 hyphae. The hyaloplasm of Mortierella reticulata and Rhizopus nigricans 

 (Moreau 1913) contracts into peculiar strands parallel to the hyphal axis. 

 The nuclei are very small throughout (1-3/a in diameter). They divide simul- 

 taneously, both directly and indirectly, in the same hyphal region. 



The hyphae generally spread out evenly within and upon the substrate. 

 Bhizopus and Absidia have more or less well-differentiated stolons, each con- 

 sisting of a node provided with appressoria or holdfasts, from which radiate 

 new stolons. The appressoria of the forms parasitic on other Mucoraceae are 

 further modified; thus in Mortierella Bainieri they grasp the host hyphae as 

 claws or spirals, and in Piptocephalis Freseniana, they penetrate the interior 

 of the hypha and there branch into a small tuft, as haustoria. 



Thick-Avalled hypnospores are formed under unfavorable conditions, while 

 in Mucor sphaerosporus the mycelium may form true sclerotia. The hypno- 

 spores usually arise endogenously ; multinucleate protoplasmic portions of 

 varying circumference draw together and, inside the original hyphal mem- 

 brane, surround themselves with a special thick wall (Fig. 3). The stipitate 

 hypnospores (mycelial conidia or stylospores) of Mortierella (Fig. 8, d) and 

 Syncephalis are cut off in scattered or racemose groups on short branches of 

 the mycelium (H. Bachmann, 1900). Under suitable environmental conditions 

 both hypnospores and sclerotia develop to new mycelia. 



Asexual reproduction takes place through sporangia with sporangiospores. 

 The parts of the mycelium from which the sporangia develop swell consider- 



