The Hemibasidii. 
36 r 
tissues of the host-plant, so that each young spore-producing cell 
comes to possess two nuclei. A fusion takes place later between 
the pair of nuclei resulting in the uninucleate chlamydospore. 
In U. Carlo, on the other hand, when several spores are 
germinating together an abundant copulation is observed not only 
between neighbouring cells of the promycelium, resembling the 
process of lateral conjugation seen in certain species of Spirogyra, 
but also between the cells of different promycelia. The sporidia 
also conjugate in pairs, or copulation takes place between a 
sporidium and a promycelial cell. Copulation is followed by the 
passage of the nucleus from the one cell into the other, so that 
the sporidia become binucleate, but no fusion of nuclei takes place 
at this stage. The sporidia germinate to produce a mycelium with 
binucleate cells, and all the cells of the hyphte within the host- 
plant were found to contain two nuclei, as well as the young 
spore-cells. The mature chlamydospore, however, possesses but 
a single nucleus, so a nuclear fusion is inferred, although it could 
not be definitely observed. 
If we compare the development of the two species of Ustilago, 
the principal difference between them consists in the fact that in 
U . Carlo the generation with paired nuclei preponderates over that 
with a single nucleus, while in U. Maydis the reverse is the case. 
According to these observations, the Ustilaginete in their 
nuclear behaviour appear to fall into line with the Uredineae and 
the higher Basidiomycetes. The view first advanced by Brefeld, 
who suggested the term Hemibasidii, that the latter with their 
promycelium consisting of a variable number of cells and producing 
an indefinite number of sporidia, represent a stage in the evolution 
of the Eubasidii, where the basidium produces a small and definite 
number of spores, receives support from cytological evidence. 
In their cytological as well as in their biological aspect, the 
Hemibasidii show the closest affinity with the Uredinere, although 
a considerably more complicated life-history is often seen in the 
latter group. In both groups the promycelium arises from a 
chlamydospore (= teleutospore in Uredinese) which is provided 
with a thick cell-wall and is often adapted to undergo a period of 
rest. The chlamydospore of both groups is binucleate in its 
young condition and uninucleate when mature. The origin of the 
binucleate condition by the copulation of two cells, not specialised 
for this purpose, is very similar in both cases. 
Again, in the Eubasidii a fusion of two nuclei always precedes 
the formation of basidiospores, although this fusion takes place 
within the basidium itself, and not in the cell from which the 
basidium arises, as is the case when it is produced by a chlamy¬ 
dospore. But this is a detail of minor importance and does not 
interfere with the homology. 
(3) Werth and Ludwigs describe briefly the development and 
germination of the chlamydospores of Ustilago antheranwi , which 
does not appear to be a favourable subject for research. They 
were unable to confirm the early binucleate condition of the spores 
described by Dangeard. 1 They assert that when the sporidia 
conjugate, the nucleus does not pass from one cell into the other. 
1 4c K. cit. 
