CHAPTER II 

 VARIATIONS IN THE LOWER FUNGI * 



Fungi, like other living things, are subject to variations in form 

 and function. Some of these are but temporary or reversible changes, 

 others are permanent; some occur spontaneously, others result from 

 the action of known environmental factors; some result from changes 

 in the hereditary constitution of a single cell, i.e., they are mutations, 

 whereas others result from an interbreeding of two races or species, 

 i.e., they are hybrids. But it is often difficult or impossible to deter- 

 mine in a given instance whether the observed change is temporary 

 or permanent, spontaneous or induced, mutant or hybrid. These 

 variations are important in explaining the origin and evolution of 

 new races and species, but as they occur in the laboratory they are 

 often very annoying, since they lead to a loss or alteration of specific 

 characters that are being studied, and lead to a great deal of con- 

 fusion in classification and nomenclature. 



Pleomorphism. If one sends to a type culture collection for cul- 

 tures of several species of dermatophytes, he is likely to receive 

 several tubes bearing different labels, but which contain molds look- 

 ing very much alike — an abundance of white woolly aerial mycelium, 

 with few or no conidia or other diagnostic characters. These molds 

 were quite different when first isolated — some powdery, some velvety, 

 some white, some colored, and wdth different types of spores. But 

 after long-continued cultivation they have gradually lost their dis- 

 tinguishing characters, becoming more and more woolly in char- 

 acter and producing more and more sterile aerial mycelium. Pig- 

 ment production is usually the first character to go. These variations 

 have been described in detail by Grigoraki.^^ 



Dermatologists, following the usage of Sabouraud, call such 

 changes pleomorphism. But this word was first used by DeBary to 

 designate the series of changes observed in rust fungi as these appear 

 on their different host plants, a phenomenon quite distinct from that 

 which we have under discussion. German mycologists have used a 

 better word, degeneration, and they have designated the change just 



* This chapter has been used as it was written by Dr. Hcnrici, with the excep- 

 tion of some minor editorial changes. 



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