3i6 Transactions British Mycological Society. 



organs which are no longer functional, and in many forms the 

 sexual organs show various stages of degeneration or have dis- 

 appeared entirely. But whether sexual organs are formed or 

 not there is always a nuclear fusion in the ascus. 



Thus in the higher forms of the Ascomycetes there may be 

 two distinct stages in the life cycle, the formation of well 

 differentiated sexual organs, and, separated from these by a 

 more or less numerous series of intermediate cell divisions, the 

 formation of asci. On the evidence before us therefore the 

 nuclear reorganisation which takes place in the ascus may have 

 nothing whatever to do with fertilisation, but may be simply a 

 means by which the vigour of the cell is restored just at the 

 period when it is probably impaired and when renewed vitahty 

 is required for the formation of the reproductive elements. 



The problem now arises: how is this phenomenon of endo- 

 karyogamy to be regarded in relation to a normal sexual act? 

 Whatever may have been the original purpose or function of 

 fertilisation it is clear that a normal fertilisation includes the 

 blending of two lines of descent, and the restoration of vigour 

 to cells which have become senescent. Hartog defines senescence 

 as "the diminution of all vigour in life, nutrition, growth, and, 

 above all, reproductive power" (Problems of Reproduction, 

 p. 22), and he has given a most interesting explanation of the 

 probable causes of senescence. The nucleus is the centre of the 

 cell, governs its life and responds to the stimulus of the cyto- 

 plasm. We may well conceive, says he, that "the nucleus during 

 the continuance of active cellular life gradually loses its readiness 

 of response to the stimulation from the cytoplasm, and with its 

 sensibihty the power to guide and control aright the functions 

 of the cytoplasm; so that the life of the cell is impaired." An 

 internal reorganisation of the cell would restore the sensibility 

 of the nucleus and the stimulatory activity of the cytoplasm, 

 and this could be effected by fertihsation. But if the primary 

 function of fertilisation or syngamy in its widest sense is merely 

 rejuvenescence, and if, in any given form, this function is the 

 only one effected by the sexual act, then it is clear that the 

 complex sexual differentiation necessary for the blending of two 

 lines of descent would no longer be required, since a complete 

 cellular reorganisation can be effected in a much simpler way, 

 by the fusion of cells and nuclei related by the closest bonds of 

 cellular kinship. 



It is therefore reasonable to conclude that if the blending of 

 two lines of descent has become, for some reason or other, super- 

 fluous, the mere reinvigoration of the reproductive cell or cells 

 may be effected by a much simpler type of nuclear reorganisa- 



