334 Olive . — Sexual Cell Fusions and Vegetative 
the formation of teleutospores ; while in the three micro species, the 
fertilization occurs at some earlier point in the life-history, without any 
immediate relation to the development of the teleutospores. 
In a second paper, Christman (’07 1 ) found that in the so-called £ primary 
uredo ’ form, Phragmidium potentillae- canadensis, the binucleated condition 
arises exactly as in the aecidium which he earlier described, by the fusion 
of two equal cells. He further emphasizes the interesting fact, also noted 
by Sappin-Trouffy, that the elongated stalk cells which bear the primary 
uredospores are plainly equivalent to the intercalary cells of the row of 
spores of the aecidium. Hence he argues that the primary uredo is mor- 
phologically an aecidium. 
Still more recently, the same author (07 2 ) has discussed the bearing 
of the facts, so far as known, on the general morphology of the various 
spore forms of the Rusts. He holds that the micro- and lepto-i orms are 
the primitive Rusts and that the teleutospores are the primitive spores. 
The various other kinds of binucleated spores in the Rusts have been, 
therefore, gradually intercalated in the life-history. Christman holds that 
the binucleated ‘ basal cell ’ (‘ basidium ’ of certain older authors) is the 
morphological unit, since each subgeneration (bearing aecidio-, uredo-, or 
teleutospores) begins and closes with such a cell. The ‘ basal cell ’ produces 
its various kinds of spores in chains, or else singly, on long stalks, by 
a process of successive budding. He therefore concludes that the various 
kinds of sporophytic spores — aecidio-, uredo- (both primary and secondary), 
and teleutospores — are all homologous structures. The spermatia repre- 
sent, in his opinion, the once functional asexual spores of the gametophyte ; 
and he points out that they are quite similar in structure and general 
appearance to the other gametophytic spores of the Rusts — the sporidia — 
as well as to the pycnidia of certain Ascomycetes. 
He finds also in Puccinia Podophylli frequent cases of the migration 
of nuclei in the teleutospore sorus from one sporophyte cell into another. 
Since no fertilization can be assumed in such instances, Christman inter- 
prets the phenomenon as purely pathological, perhaps due to the wound 
received at the time of fixation. He is therefore inclined to interpret 
Blackman’s nuclear migrations in the vegetative cells at the base of the 
aecidia of Puccinia Poarum , as well as in other cases, as occurrences of 
a similar pathological nature. 
The process of nuclear division in the Rusts is much better known 
for the nuclei in the promycelium than for the vegetative nuclei. Poirault 
and Raciborski (’95) studied the nuclear divisions in various types of cells 
of the group, and have obtained some very exceptional results. Each 
nucleus is regarded as containing but a single chromosome, which, during 
mitosis, splits longitudinally. During conjugate division, the two dividing 
nuclei form, in their opinion, but one spindle. 
