404 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
In the case of the rusts Rosen (1892) saw two nuclei in the scidio- 
spore of certain species. Dangeard and Sapin-Trouffy (1893) reported 
the occurrence of a nuclear fusion in the teleutospore. Sapin-Trouffy 
(1896) found that the cells of the excidium-bearmmg mycelium are 
uninucleate up to the very base of the chain of ecidiospores. Maire 
(1900) first stated clearly the whole nuclear cycle in rusts: Beginning 
with the binucleate ecidiospore there follows, e. g., in the wheat rust, 
the uredo or rust stage, which has a binucleate mycelium and forms 
binucleate uredospores for several generations. The two nuclei of 
the young teleutospore, finally formed on this mycelium, fuse as the 
spore matures. The two divisions of this fusion nucleus in the 
promycelium give rise to the four nuclei of the four sporidia which 
germinate to the uninucleate cluster cup mycelium on the barberry. 
Maire saw in this life history a real alternation of generations, the 
gametophyte or X generation beginning with the sporidium, the 
sporophyte or 2X generation, with the mother cell of the ecidiospore 
chain. 
Blackman (1904) and Christman (1905) discovered the origin of 
the binucleate condition of this mother cell in species of Phragmidium. 
It there arises by the migration of a nucleus from one cell into another, 
or by the fusion of the cytoplasm of two cells to form the mother cell 
of the spore chain. The two nuclei thus brought together divide 
simultaneously or conjugately, each contributing a nucleus to the 
first and to each succeeding spore. This conjugate division of the 
paired nuclei and their descendants was shown to occur all through 
the uredo generation up to the formation of the young teleutospore. 
In the interpretation of their discoveries Blackman and Christman 
differ more widely than in the facts reported. The former supports 
the surmise of Meyen, and believes the basal cells of the spore chain 
are oogonia which were primitively fertilized by the now functionless 
spermatia, or pycnospores, that are produced in separate organs on 
the barberry leaf. Christman, on the contrary, regards the fusing 
cells at the base of the eciditum as the primitive, undifferentiated 
sexual organs of these fungi. He holds that male and female organs 
have never become differentiated in this group, and thinks that the 
spermatia are, or were, propagative cells of the X generation. 
The observations of many workers on the smuts and on the toad- 
stools have shown the frequent occurrence in them of an association 
of nuclei and the final fusion of two nuclei in the chlamydospore or 
the basidium. The time and mode of association of the fusing nuclei, 
or of their progenitors, are very different in different forms. The 
fusion, and what appear to be the reduction divisions are, however, | 
constant in location in each species, and are always closely associated. 
Thus, the nuclear fusion in the smuts often occurs in the chlamy- 
dospore, according to Dangeard (1893) and Rawitscher (1912), and 
