CHAPTER II 



THE SEXUALITY OF THE UREDINALES 



De Bary suggested in 1884 that, if there was any sexual act 

 occurring in the life-cycle of the Uredinales, it would probably 

 be found in connection with the aecidium. At that time 

 nothing was known on this point, and De Bary anticipated that 

 something might take place analogous to what happens in the 

 formation of the asci of certain Ascomycetes. 



The first discovery was made by Blackman (1904), who 

 found that, in laying the foundation of the spore-bed of the 

 secidium of Phragmidium violaceum, cells became binucleatc 

 by the passing into them of a 

 nucleus from an adjoining vege- 

 tative cell. He saw that this 

 passage took place through a nar- 

 row opening formed between the 

 cells (Fig. 18). The bi nucleate 

 cell then became the equivalent 

 of an oospore, and formed the be- 

 ginning of a sporophytic genera- 

 tion. In other words, he supposed 

 that the fertilised cell represented 

 a female gamete and the vegeta- 

 tive cell replaced a now vanished 

 or functionless male gamete. The 

 fertilisation would then be of the 

 nature of a semi-apogamy. He 

 considered that the spermatia 

 were the functionless male gametes. From the cell to be 

 fertilised he saw an upper sterile cell cut off, which soon 

 G. u. 2 



Fig. 18. Phragmidium violaceum. 

 Development of *cidium (after 

 Blackman) ; e, the epidermal 

 cells ; s, sterile cells ; in the hasal 

 cells below, a nucleus is seen 

 migrating into a fertile cell, /'. 



