THE SEXUALITY OF FUNGI.* 



HAROLD WAGER, F.R.S. r ,;, 



The varied phenomena of sexual fusion in the Fungi open up 

 some extremely interesting problems concerning the significance 

 of sex. During the last 25 years, the cyotlogical features of 

 the nuclear fusions which take place in the Fungi have been 

 very fully investigated, with the result that in certain forms, 

 such as Peronospora and Cystopus, a very distinct sex differ- 

 entiation obtains, which closely resembles that found in the 

 higher organisms. In other groups, however, Ascomycetes, 

 Uredineae, and Basidiomycetes, there is a modification of the 

 sexual process resulting in the fusion of two nuclei which are 

 found in one and the same cell, Ascus, Teleutospore, or Basidium. 

 In the case of the teleutospore the two nuclei can be traced 

 back through a long series of generations to the Aecidium, and 

 here Blackman has found that the binucleate condition arises 

 by the fusion of two cells. In the Ascomycetes, on the other 

 hand, the two nuclei of the Ascus cannot be traced back 

 in this way, but there is, in some forms, a previous fusion 

 of two sexually differentiated cells. Whether these two fusions 

 in the Ascomycetes are genetically connected is not known, but 

 there is strong evidence to show that the first fusion is a process 

 of degeneration and in some forms has entirely disappeared, 

 leaving only the fusion in the Ascus. In the Hymenomycetes 

 there is only one nuclear fusion, and this takes place in the 

 basidium. This means that in this large group of the Fungi 

 about gooo species, there is no true sexual fusion and no blending 

 of two lines of descent. 



The well marked sexuality which exists in the lower groups 

 of Fungi is, therefore, being replaced, in the higher groups, 

 by a reduced or apogamous fertilization. What advantage or 

 disadvantage this may be, we cannot say ; we require more 

 knowledge of the significance of sex in the higher organisms 

 before we can attempt to answer the question, but it is an inter- 

 esting fact that this autogamous fertilization should occur in 

 a group in which there is an extraordinary amount of variation. 



At the meeting of the Vertebrate Section of the Yorkshire Naturalists' 

 Union to be held at the Leeds Institute on November i6th. Dr. Heather- 

 ley will deliver a lecture on ' The Life History of the Peregrine Falcon,' 

 which will be illustrated by an exceptionally fine series of photographs. 

 The birds referred to were watched continuously for some weeks without 

 a break, so that there is a remaikably unbroken series of notes thereon. 

 Several members of the Yorkshire Naturalists' Union took part in the 

 observations. 



* Abstract of Lecture deHvered at the meeting- of the Mycologrical 

 Section of the Yorkshire Naturalists' Union at Sandsend, Sept. 28th to Oct. 



3«'d- 



Naturalist, 



