Sexual Cell Fusions and Vegetative Nuclear Divisions 
in the Rusts. 
BY 
EDGAR W. OLIVE. 
With Plate XXII. 
W E owe to the recent important discoveries of Blackman (’04) and 
Christman (’05) our knowledge as to the existence of a process 
of sexual reproduction which occurs at a certain stage in the development 
of the Rusts. Their accounts conflict somewhat, however, in respect to 
the mode of origin of the binucleated condition ; hence the need of still 
further work on the cytology and minute structure of these forms. The 
following research explains to a certain extent some of the discordant 
results of the two accounts just mentioned, and at the same time extends 
our rather limited knowledge of the nuclear division in the vegetative 
cells. Further, the discovery of multinucleated cells at the base of certain 
aecidia, which may possibly be identical with the archicarps of De Bary, 
Massee, and Richards, obviously shows the urgent need of an investigation 
of the structure and development of further types of the aecidium-cup, 
before we shall be able to understand the possible connexion of this type 
of fructification with the simpler caeoma type, as well as its relationship to 
the fruit-bodies of other Fungi and Algae. 
Earlier views as to the way the binucleated cells have arisen have been 
sufficiently reviewed in the papers of the writers just mentioned ; hence 
a brief summary here will suffice. Rosen (’92) regarded the two nuclei in 
the aecidiospores as sister nuclei. The basal cell of the row of spores 
starts, according to him, with one large nucleus, which divides, and the 
upper of the two resulting daughter-nuclei at once divides again, this time 
at right angles to the axis of the elongated cell. The two nuclei thus 
formed in the apical end of the basal cell are then cut off by a cross wall 
from the one nucleus below, and thus form the beginning of the binucleated 
series. The uninucleated basal cell left below proceeds to divide again, 
and another binucleated cell follows as described. 
Poirault and Raciborski (’95) apparently thought that the binucleated 
condition started in the sporidium, which they found sometimes contained 
two nuclei. They emphasized the fact, however, that the two nuclei which 
finally fuse in the teleutospore have no close relationship, since each has 
[Annals of Botany, Vol. XXII. No. LXXXVII. July, 1908.] 
A a 
