WHAT FUNGI HAVE PHYSIOLOGIC SPECIALIZATION? 259 



are not sufficiently distinct morphologically to entitle them to 

 specific rank but must be distinguished from each other by 

 pathogenic reactions. 



If the worker is dealing with fungi that can be cultivated on 

 artificial media, he may employ differences in cultural character- 

 istics, for example, in color of mycelial mat, shape of colonies, 

 surface markings, size of colonies, branching of hyphae, and 

 abundance of conidia, to distinguish physiologic forms. This 

 situation is typified by the cultural differences noted by Chris- 

 tiansen (1932) in the 15 races of Pestalozzia fwierea that he iso- 

 lated from needles of longleaf pine. These races differed in 

 abundance, color, and zonation of surface and aerial mycelium, in 

 abundance, distribution, and size of acervuli, and in size, shape, and 

 color of spores. 



Several other terms, including variation, mutation, saltation, and 

 dissociation, have been more or less loosely used in connection 

 with the phenomenon of differences among the members that 

 comprise a given species of fungi. For clarity these terms may 

 at this point be defined. Variation is applied to divergences, 

 whether morphological or physiological, from the observed char- 

 acteristics of the usual or normal condition. They are regarded 

 as non-hereditary. Variation is usually regarded as svnomvmous 

 with dissociation. Mutation, as originally employed by de Vries, 

 refers to sudden variations, the offspring differing from the par- 

 ents in one or more clearly defined characteristics. Mutation is 

 to be distinguished from gradual variation, such as may occur 

 during the course of countless generations. Furthermore muta- 

 tions are hereditary, since once they appear, they can be trans- 

 mitted to the progeny. Saltation may be defined as a type of mu- 

 tation that appears in artificial cultures. Saltations may be main- 

 tained indefinitely in subcultures if conidia or hyphae are used in 

 transplantation. Sports, as the term is applied to seed plants that 

 can be propagated by cutting or other vegetative structures, cor- 

 respond to saltants among fungi. 



In what fungi has physiologic specialization been observed? 

 Numerous species of pathogenic fungi are known to consist of 

 many physiologic forms. Presumably all do. At least, it would 

 be scientific news if after extensive study one was found that was 

 not comprised of numerous physiologic forms. 



