The Uredinece. 
*33 
Christman (’05) confirms the work of Blackman as to the 
association of nuclei but differs very much as to the details. He 
finds that the fertile cell bearing two nuclei is the result of a 
conjugation of two previously differentiated gametes and his figures 
seem very conclusive (Christman, Figs. 1-8). He also agrees with 
Blackman in regarding this as a sexual process. The result of the 
research of these two investigators has been to place the sexuality 
of the rusts beyond further question. 
This brings us to some interesting observations concerning the 
nature of the mycelium of this generation. If the aecidium is to be 
regarded as a collection of female sexual organs, then the mycelium 
which produced it is a gametophyte. Since the spermogonia and 
the aecidia are produced in the same mycelium then we have further 
reason for believing that the spermatia are functionless male 
gametes, a view which hns been held by many investigators since 
the earliest time. The nature of the spermatia, however, remains 
uncertain, as well as the question whether the manner of sexual 
union in the aecidium is a derived or a primitive one. 
The Transition from the Binucleate to the 
Uninucleate Generation. 
If we regard the association of nuclei in the aecidium as a 
complete sexual process, then what importance must we assign to 
the fusion of the nuclei in the teleutospore ? Blackman has suggested 
that this fusion is in the nature of the reduction division in the 
higher plants. He accordingly regards the teleutospore as the 
analogue of the spore mother-cell. Maire and others have regarded 
the fusion as the completion of a sexual process which began in the 
yecidium but has been greatly prolonged. Holden and Harper 
were inclined toward the view that the fusion in the teleutospore 
is a sexual process. It seems to me very reasonable that the two 
nuclei which fuse in the teleutospore simply complete the sexual 
process and that the mature teleutospore is as Blackman suggested 
a spore mother-cell. It is therefore the last cell of the sporophyte 
and the first division of the spore is the analogue of the heterotypic 
division of the higher plants and that the formation of the 
promycelium is analogous to the formation of the spore tetrad. 
These cells then are the first cells of the gametophyte. 
There is, therefore, a definite alternation of generations as 
clearly marked as in any of the higher plants and based on the 
same essentials, namely the reduction of the number of chromosomes 
