4 8 RESEARCHES ON FUNGI 



as a result of observations and experiments made by Harder, the 

 effect of the nucleus on growth has been placed beyond doubt. 



Harder * observed that, in Pholiota mutabilis, the rate of growth 

 of a diploid mycelium (two nuclei in each cell) is about twice as 

 great as that of either of the two haploid mycelia (one nucleus in 

 each cell) from which it has been derived. By micro-dissection of 

 hyphae in the state shown in Fig. 22, A, he isolated uninucleate 

 penultimate cells and afterwards succeeded in getting them to grow 

 and to develop into haploid mycelia. He then found that these 

 artificially produced haploid mycelia had a rate of growth of only 

 about one-half that of the diploid mycelia from which they had come. 

 This difference in growth-rate can readily be explained on the 

 supposition that the amount of nuclear material in a cell of Pholiota 

 mutabilis affects the rate of growth, a conjugate pair of nuclei 

 causing the cytosome to grow in length about twice as fast as a 

 single nucleus. 



The solution of the problem of the biological advantage accruing 

 to a diploid mycelium from the arrangement that the hooks of the 

 clamp-connexions grow backwards instead of forwards seems to 

 follow naturally from Harder's work and may be stated thus. If 

 the hook of each clamp-connexion were to grow forward, the terminal 

 cell of each hypha, in which alone growth in length takes place, 

 would periodically (during the formation of each clamp-connexion) 

 have its nucleoplasm^ ratio upset to the extent of being reduced to 

 one-half, thus affecting growth adversely ; whereas, when the hook 

 grows backwards, as is actually the rule, there are always two 

 nuclei in the terminal cell and the nucleoplasmic ratio is never 

 greatly disturbed and remains relatively constant. 



Mile Bensaude's Second Mode of Formation of a Clamp- 

 connexion unconfirmed.— Mile Bensaude, 2 as a result of her cyto- 

 logical investigations on Coprinus lagopus (her C. fimetarius), con- 

 cluded that clamp-connexions in this species are formed in two 

 ways : (1) as shown in Fig. 21 (p. 45), and (2) as shown in Fig. 23. 



1 R. Harder, " Zur Frage nach der Rolle von Kern und Protoplasma im Zell- 

 geschehen und bei der Ubertragung von Eigenschaften," Zeitschrift fur Botanik, 

 Bd. XIX, 1927, pp. 350-351. 



2 Mathilde Bensaude, Joe. cit., pp. 64-66. 



