Significance of Sex and Nuclear Fusions. Harold Wager. 315 



aecidium it takes place in the cells at the base of the young 

 aecidium. Maire described in some species a re-duplication of 

 the nuclei by the division of the single nucleus of uninucleate 

 terminal cells of hyphae below the aecidia. But this has not 

 been confirmed and is, no doubt, from the evidence afforded by 

 more recent observations, incorrect. Blackman found that cells 

 become binucleate by the migration of a nucleus from one cell 

 to another, and Christman showed that it might also be effected 

 by the fusion of two cells. In the absence of an aecidial stage 

 cell fusion may take place in the vegetative cells at the base of 

 the uredosporcs or teleutospores. In Uromyces Scillarum (Grev.) 

 Madame Moreau believes it may take place somewhere in the 

 vegetative mycelium. 



The cellular fusion at the base of the aecidium probably takes 

 the place of an ancestral fusion of normal sexually differentiated 

 gametes. Blackman suggests that this may be characterised as a 

 vegetative fertilisation. After a more or less prolonged period 

 of vegetative growth, during which the cells maintain their bi- 

 nucleate condition, large numbers of teleutospores are formed, 

 each of which receives two nuclei ; these ultimately fuse, and 

 this is held to be the final stage in a sexual fusion which began 

 by the fusion of cells in the aecidium. But this does not seem 

 to me to be a satisfactory explanation of what takes place. 

 The binucleate condition of the vegetative cells is a necessary 

 preliminary to endokaryogamy in the teleutospore,but the result 

 would be the same in whatever way the cells might become 

 binucleate. We may regard the fusion of the cells in the aecidium 

 as the result of a degraded or vegetative sexual differentiation, 

 or simply as the fusion of somatic cells, taking the place of the 

 original fusion of sexually differentiated gametes. It is not 

 necessarily connected with the original sexual act, but may be 

 a new type of cell fusion brought about in order to provide 

 the binucleate condition of the vegetative cells necessary for 

 endokaryogamy. The significant phenomena in this new type 

 of fusion are the nuclear fusion and the subsequent reducing 

 division in the teleutospore which provide just that new 

 cytoplasmic and nuclear association upon which the stimulus 

 necessary for the rejuvenescence and continued development of 

 the organism depends. 



In the Ascomycetes we have perhaps the clearest indication 

 that a normal sexual fusion is being replaced by endokaryo- 

 gamy. In some forms there are well-developed sexual organs, 

 and, if Harper's observations are correct, a normal sexual fusion 

 of nuclei, comparable in all respects with the sexual nuclear 

 fusions in the lower Fungi. Others possess well-developed sexual 



