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James R. Weir. 
The life history having been thus briefly stated the special 
significance of certain phases will now be discussed more in detail. 
The Transition from the Uninucleated to the 
Binucleate Generation. 
As previously stated the uninucleated condition begins with 
the teleutospore and continues until the aecidium is reached, where 
the transition to the binucleated state is effected. This important 
condition in the life history escaped the notice of investigators 
until about ten years ago, when it was first pointed out by Sapin- 
Trouffy. Although he did not reach the ultimate conclusion of the 
significance we now attach to all of the details, we must still give 
him the credit for having placed us on the right road to a complete 
understanding of the life history of the rusts. It remained for 
Blackman, and later for Christman (’04), to supplement the work 
of Sapin-Trouffy by extensive research aimed particularly at the 
nature of the secidium and to point out the true nature of the 
transition. 
Blackman in his masterly review of this subject laid especial 
emphasis on the manner in which the first binucleated cell is 
produced. Marie had previously held that it originated by a single 
division of the nucleus of a vegetative cell, that these nuclei 
were therefore sisters and that they continued to divide by conjugate 
division until the teleutospore was reached where they fuse. He 
accordingly placed much more emphasis on the fusion in the 
teleutospore than he did on the first division which gave rise to a 
cell with two nuclei. 
Blackman’s research, however, gives us an entirely new and 
much more satisfactory method of the origin of the first binucleated 
cell. He finds that a migration of nuclei takes place into the cells 
which have first become slightly differentiated and to which he 
gives the name fertile cells. The migrating nucleus may come 
from a cell directly below the fertile one in the same filament or 
from an adjacent cell in a different filament. The two nuclei in a 
fertile cell are therefore not sisters, and their association in the 
cells has very much the appearance of a sexual process. He states 
very positively that this has practically all of the essential 
characteristics of a true sexual process and he therefore attaches 
very little significance to the fusion in the teleutospore. In this 
he is directly opposite to Sapin-Trouffy who regarded the fusion 
in the teleutospore as a sexual process. 
