246 THE AMERICAN NATURALIST. . [Vor. 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, 
'04—95a, c; Poirault and Raciborski, '95 ; Sapin-Trouffy, '96; 
Maire, :00 a, b, c, :02; Holden and Harper, :03) that the 
ecidiospores 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 fora 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; :00) 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 Gymnosporangium 
