232 



INTRODUCTION TO CYTOLOGY 



and the mycelia developing from them are of two kinds, only those of 

 unlike strain ("plus" and "minus") uniting when brought together.^^ 



The significance of the hyphal and sporidial fusions which lead to 

 the binucleate condition of the cells in the dikaryophase of ascomycetes 

 and basidiomycetes is a matter of debate among mycologists. The view 





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fir 





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FiG. 140. — Syngamy in Riccardia. 1, sections of spermatozoids in archegonium; one 

 male nucleus applied to egg. 2, male nucleus in egg cytoplasm. 3-7, passage of male 

 nucleus into egg nucleus and its development of a distinct reticulum. 8, 9, first mitosis in 

 zygote; paternal and maternal chromosomes intermingled. {After Showalter, 19266.) 



that they represent a sexual act is disputed by those who hold that they 

 are primarily nutritive in character ("nutritive heterothahism"), 

 although they may be followed by some of the beneficial effects of true 

 sexuality. Comparisons with other plants strongly suggest that sexual 

 differences in fungus nuclei and mycelia, as well as other conditions 

 affecting their interaction, are often related to meiotic factor segregation 

 in sporogenesis. This topic is discussed further at page 386. 

 15 Kniep (1919, 1920), Stakman and Christensen (1927), Hanna (19296). 



