246 THE AMERICAN NA TURALIST. [Vol. XXXIX. 



the unions of the pairs of nuclei which enter the cells of the 

 developing teleutospores of the Uredinales and Ustilaginales 

 and the basidium of higher Basidiomycetes. It has been estab- 

 lished through the studies of a number of investigators (chiefly 

 Rosen, '93 ; Dangeard and Sapin-Trouffy, '93 ; Dangeard '93, 

 '94-'9Sa, c ; Poirault and Raciborski, '95 ; Sapin-Trouffy, '96 ; 

 Maire, : 00 a, b, c, : 02 ; Holden and Harper, : 03) that the 

 aecidiospores and the mycelium derived from them and pre- 

 ceding the development of the uredospores and teleutospores 

 contain pairs of nuclei which divide in such a manner (conjugate 

 division) that the nuclei of the pair are derived through two 

 unbroken lines of succession for a long vegetative period and 

 always maintain complete independence of one another. Every 

 young teleutospore and basidium contains such a pair of nuclei 

 which shortly fuse so that the mature structure is uninucleate. 

 Dangeard and Sapin-Trouffy have from the first regarded the 

 nuclear fusion within the teleutospore, whether of rust or smut, 

 as a sexual act and the ripe teleutospore a fertilized egg, regard- 

 less of the fact that its morphology was not that of any known 

 sexual organs. Dangeard ('94—95 c; :oo) likewise considered 

 the nuclear fusions in the basidium as sexual. Raciborski ('96) 

 suggested that the series of conjugate mitoses leading to the 

 nuclear fusions in the teleutospore represented a vegetative 

 phase intercalated between the beginning 'of a sexual act and its 

 finish in the teleutospore. His explanation, in the light of the 

 recent paper of Blackman (:04a), was nearest the truth. Maire 

 (: 02) presents the most extensive account of the nuclear struc- 

 ture in the higher Basidiomycetes previous to and during the 

 formation of the basidia. He held that the fusion of the paired 

 nuclei (synkaryon) in the basidium was not the whole act of 

 fertilization which must begin with the formation of the paired 

 nuclei. Maire (: 02, p. 189) gave some suggestions as to how 

 and where the paired nuclei arose but neither he nor any of the 

 authors mentioned above knew clearly their origin. 



Blackman (: 04a) has made the most important contribution to 

 the subject of fertilization and alternation of generation in the 

 Uredinales, showing clearly that the paired nuclei appear in the 

 life history of Phragmidium violaceum and Gymnosporangiutn 



