PARASITISM AND RESISTANCE 385 



for the survival of the ah-eady formed fungus colonies. Connections are 

 then made by anastomoses of the hyphae from the insect and the hyphae 

 of the fungus crust under which the insect has come to rest. Thus, the 

 fungus colony does not originate from one individual but from the aggre- 

 gation of several individuals by anastomosis, or grafting. The parasitized 

 insects are dwarfed and do not reproduce but may live as long as the 

 uninfected insects. The fungus covers the insect's body but is in contact 

 with it only by the numerous coiled haustoria. The insect in turn 

 receives protection from severe weather conditions, from parasitic wasps, 

 other insects, and birds. Certain species, particularly S. hurtii, are easily 

 cultivated on liquid or agar media. Couch believes that failure of the 

 fungus to fruit in culture may be due to lack of proper nutrition, which 

 is furnished by insects in nature, or to a complicated heterothallic condi- 

 tion of the fungus. 



Fungi parasitic on other fungi. The parasitic habit of many of the 

 chytrids upon other aquatic or semiaquatic fungi and algae is apparently 

 quite common. A number of these genera are described and illustrated 

 by Fitzpatrick (1930) and Karling (1942). Practically nothing is known 

 regarding their nutritional requirements. There appear to be fewer 

 filamentous fungi parasitic upon fungi. The mention of only a few of 

 these will serve as examples. Species of Piptocephalis, Chaetocladium, 

 and Syncephalis are parasitic on other Mucorales. A number of fungi are 

 reported to be parasitic on members of the Agaricaceae and other higher 

 fungi. Among these are species of Spinellus, Mycogone, Hypomyces, 

 Nyctalis, and some Myxomycetes. A species of Penicillium is parasitic 

 upon an Aspergillus (Thorn and Raper, 1945). Of particular interest 

 are the hyperparasites, fungi parasitic upon other parasitic fungi. Cicin- 

 noholus cesatii is parasitic on the Erysiphales, and Darlucafilum is parasitic 

 on Uredinales. So far as is known, no study of the basic nutritional 

 requirements of these fungi has been attempted. 



Fungi parasitic on man and animals. Many of the fungi which cause 

 disease of man and animals show distinct differences in morphology when 

 grown under different conditions. The spore forms produced on artificial 

 media may be quite different from those developed in the host. This 

 may be a response to certain nutritional factors, to temperature differ- 

 ences, or to the presence of certain chemical substances which inhibit 

 or limit the production of certain spore forms. 



In general, the pathogens of man and animals have no unique nutri- 

 tional requirements. Some are able to utilize inorganic nitrogen, while 

 others are not; some are deficient for certain vitamins. Nickerson (1947) 

 points out that there is no direct correlation between nutritional require- 

 ments and pathogenicity. In fact, there is little concrete evidence 

 regarding the mode of action of these fungi in causing disease. 



