Lutman—Life History and Cytology of the Smuts. 1221 
Tilletia and its related genera are presumably more special¬ 
ized than is Ustilago and it is interesting to note that the binu- 
cleated condition is present in them at an earlier stage preced¬ 
ing spore formation. This may well be due to the working 
back of the binucleated condition in the life cycle from the 
spore in which only it is present in Ustilago. 
That the sporophytic binucleated condition of the cells can 
work back in the mycelium has been recently shown by the work 
of Maire (31) on Galactinia succosa in which he found that 
the binucleated condition which was supposed to appear only 
in the ascus cell may appear in several cell generations back of 
it. Such a tendency might lead to a form with binucleated cells 
throughout its ascogenous hyphae and this condition might lead 
to the entire suppression of the original type of fertilization 
such as occurs in Pyronema, Sphaerotheca, etc. according to the 
work of Harper (19, 20, 23). The old, normal fertilization at 
the beginning of the sporophyte generation might thus become 
lost or suppressed. 
In the rusts this may have happened. The binucleated con¬ 
dition of the teleutospore with conjugate divisions may have 
worked its way back until, as we find, the entire mycelium of the 
sporophytic generation is composed of binucleated cells. In the 
Basidiomycetes the process apparently has not gone so far. In 
them, as Miss Uichols (32) has shown, the binucleated condi¬ 
tion does not arise at any one region in the mycelium but may 
start at almost any point in it. 
In this connection the fusion of the cells in the promycelium 
of Ustilago is interesting. These fusions are entirely similar to 
those in the yeasts but in them the fusion leads to different re¬ 
sults. In the yeasts the fusion is evidently a sexual process ac¬ 
cording to the accounts of Barker (1) and Guilliermond (17 & 
18). It may lead to the production of ascospores or as in Sac- 
charomyces Ludwigii it may occur at their germination. In 
the smuts also the process has all the appearance of being sex¬ 
ual ; the fusion typically occurs in pairs; there is an apparent 
attraction of the nuclei for each other and a fusion of the nuclei 
m some cases. 
