CHAPTER II 



THE EFFECT OF DIPLOID ON HAPLOID MYCELIA IN COPRI- 

 NUS LAGOPUS, AND THE BIOLOGICAL SIGNIFICANCE OF 

 CONJUGATE NUCLEI IN THE HYMENOMYCETES AND 

 OTHER HIGHER FUNGI 



Introduction — Definition of the Terms Dlploidisation and Diploidise — Coprimts 

 lagopus — Methods — Criteria of Sex — Tfie Four Kinds of Haploid and the Two 

 Kinds of Diploid Mycelia— The Pairing of Haploid and Diploid Mycelia— The 

 Rate of Movement of Nuclei through a Haploid Mycelium which is being 

 diploidised by (1) another Haploid Mycelium or by (2) a Diploid Mycelium — 

 Direction taken by Nuclei in passing through a Haploid Mycelium which is 

 becoming Diploidised— A Sex-factor Analysis of a Diploid Mycelium derived 

 from a Large Haploid Mycelium which has been diploidised by a Small Diploid 

 Inoculum — Observations on the Conversion of Haploid into Diploid Hyphae — 

 The Number of Radial Hyphae of a Large Haploid Mycelium which are 

 converted into Diploid H;yphae through the Action of a Suitable Haploid 

 or Diploid Inoculum — The Frequency of Conjugate Nuclear Division in a 

 Radial Diploid Hypha — Hyphal Fusions between All Possible Kinds of Mycelia 

 — The Dlploidisation of a Haploid Mycelium by a Theoretically Incompatible 

 Diploid Mycelium — The Biological Significance of the Dlploidisation of a 

 Haploid Mycelium by a Diploid Mycelium — The Biological Significance of 

 Conjugate Nuclei 



Introduction. — In the great group of fungi known as the Basidio- 

 mycetes, which inchides the Hymenomycetes, the Uredineae, the 

 Ustilaginaceae, and the Tilletiaceae, when two haploid myceha (or 

 their equivalents) of opposite sex unite, two nuclei of opposite sex, 

 each nucleus containing n chromosomes, come together in one cell. 

 However, as a rule, the two nuclei do not unite but remain as a pair 

 of nuclei, {7i)-\-{n), and they divide at one and the same time, 

 so that one pair of nuclei gives rise to two daughter pairs. Such 

 a yoked division of two nuclei is known as conjugate nuclear division. 

 In the fungi under discussion, when once a pair of conjugate nuclei 

 has been formed, scores or hundreds of successive conjugate nuclear 

 divisions may follow with the result that, in the end, many thousands 



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