270 PHYSIOLOGIC SPECIALIZATION AND VARIATION 



more, that such differences may be correlated with the existence 

 of physiologic races of the particular species is shown by the 

 experiments of Goulden, Newton, and Brown (1930). Among 

 the 16 form species of Puccinia graminis tritici that they used 

 some were more pathogenic on wheat in the seedling stage than on 

 the same variety in the mature condition. 



Environmental factors and variation among saprophytes. 

 Variations among saprophytic fungi, in relation to their produc- 

 tion by such factors as temperature, chemicals, kind and amount 

 of food, and effects of radiations, have also been given due con- 

 sideration. An appreciation of the influence of environmental 

 factors is shown in the report by Barnes (1936). In it he states 

 that Hansen, in his work with yeasts in 1883, was the first to in- 

 duce variation in a fungus. He secured an anascosporous yeast 

 by use of high temperature. In Barnes' own studies, involving 

 Eurotium herbariorum, Botrytis cinerea, and Thamnidium elegans, 

 he secured variants by exposure to temperatures just insufficient 

 to kill. These variations were manifest by reduced fertility or 

 less vigorous vegetative development. Barnes judiciously indicates 

 the need for distinguishing between modifications that are tempo- 

 rary in nature and variants characterized by permanency. Both 

 modificatory types appeared in his own experiments and in those 

 of certain others. Barnes' (1936) discussion involves the possibil- 

 ity that wounding which results from breaking the hyphae while 

 making transfer from one medium to another may induce varia- 

 tion. He would not attribute all variation to nuclear changes, 

 since physiological processes might conceivably be deranged 

 without nuclear derangement. Barnes concludes by saying, 

 "Variants are damaged versions of the normal stocks . . . and the 

 evolutionary process may depend in part on the running down 

 of the biological machine." 



Evidence presented by Barnes (1928, 1930) shows that variation 

 can be induced in Eurotium herbariorum and Botrytis cinerea by 

 subjecting the spores to high temperatures. In E. herbariorum 

 these variations are manifest by differences in amount of aerial 

 mycelium, density of growth, color of conidia, and abundance 

 of perithecial formation; in B. cinerea, by the change in color 

 and density of the mycelium and by abnormalities in abundance 

 of conidia and sclerotia. Certain variants that arose by high-tem- 

 perature treatment seemed capable of retaining these characteristic 



