408 PHYSIOLOGY OF THE FUNGI 



leucine, lysine, methionine, phenylalanine, proline, threonine, trypto- 

 phane, and valine. 

 Beadle (1946) states: 



The list of compounds that Neurospora can be made to require from an external 

 source is remarkably similar to a list of chemicals that we cannot make and 

 require in our food suppl3^ It is clear, therefore, that the substances the bread 

 mold needs in its metabolism are very much the same as those we need. The 

 difference is only an apparent one and results from the fact that bread mold 

 makes them whereas we let some other organism make them for us. By inacti- 

 vating the right genes the bread mold can be made very similar to man in its 

 nutritional requirements. 



Using a technique similar to that described above for Beadle's work, 

 Bonner (1946) exposed conidia oiPeniciUium. notatum and P. chrysogcmnn 

 to X rays and ultraviolet rays. Of a total of 85,595 "strains" tested, 

 398 were found to be deficient in synthetic ability. Since these species 

 of PeniciUium are imperfect, the genetic basis for the biochemical changes 

 cannot be proved, but it seems likely that this is the case, just as in 

 Neurospora. 



Inheritance in the Basidiomycetes. In the life cycle of the Basidio- 

 mycetes there exists a distinct diploid (dicaryotic) vegetative phase of 

 extended duration, in which the cells usually contain two haploid con- 

 jugate nuclei. Buller (1941) cites the results of numerous experiments 

 by himself and others to furnish ample proof that one nucleus of the 

 conjugate haploid pair in the diploid mycelium may affect the expression 

 of the other nucleus and thus exhibit dominance. This is true for physio- 

 logical as well as morphological characters. Experimental evidence 

 indicates that the genetic behavior of a cell containing two conjugate 

 haploid nuclei is similar to that of the diploid nucleus, if the two were 

 fused. Buller believes that the term "diploid cell" can apply equally 

 well to a cell containing two conjugate haploid nuclei and to a cell con- 

 taining one diploid nucleus. He prefers to use the terms "haploid" and 

 "diploid" in describing mycelium or cells to the terms "monocaryotic" 

 and "dicaryotic" which are also in use. We prefer to follow Buller in 

 the use of these terms. 



In the higher Basidiomycetes, principally the Agaricales, genetic studies 

 have been chiefly limited to the inheritance of sex factors or compatibility 

 factors. Fewer studies have dealt with the more strictly physiological 

 characters. In a heterothallic species, two compatible haploid mycelia 

 unite to initiate the diploid mycelium, which in many species is recog- 

 nized by the presence of clamp connections. Usually, the formation of 

 the diploid mycelium is a prerequisite to the production of fruit bodies. 



Exidia, in the Tremellales, Avill serve as an example of the higher 

 Basidiomycetes. In four species studied (Barnett, 1937) the single- 



