26 
V. H. Blackman. 
and the aecidia collections of female reproductive organs in 
P. violacewn, and therefore in the whole group, it becomes clear that 
the Uredineae present an alternation of generations which is as- 
sharply marked as that of the higher plants. For not only can the 
two generations be distinguished as sexual and asexual, but they are 
also to be cytologically differentiated by the possession of single and 
paired nuclei, respectively. The gametophyte generation starts 
with the uninucleate teleutospore which seems to correspond with 
the spore-mother-cell, and like it is followed by a tetrad division by 
which the four sporidia are produced ; from these the mycelium of 
the gametophyte develops and produces later the spermogonia and 
aecidia. The fertilised cell in the aecidium starts the sporophyte 
generation with paired nuclei, from which the aecidiospores almost 
immediately arise ; the sporophyte mycelium bears later uredospores 
and finally teleutospores. 
The fusion of nuclei in the teleutospore cannot then be looked 
upon as a process of fertilisation, but merely as the secondary 
process which brings about the disappearance of the special cyto- 
logical conditions initiated by fertilisation, i.e. change from the 
sporophytic to the gametophytic condition; it must accordingly be 
looked upon as a reduction-process. Like the reduction-process in 
the higher plants it is followed by a tetrad division. 
A careful study of nuclear division in the two forms in question 
shows, that in all the divisions except those in the promycelium, it 
is of such a simple, no doubt reduced, type that chromosome- 
formation is in complete abeyance ; it becomes then impossible to 
assert that reduction in number of nuclei in the teleutospore is also- 
associated with reduction in the number of the chromosomes. In 
the promycelium, however, the divisions are much more typical, for 
a well-marked spindle with centrosomes and polar radiations was 
observed, the spindle being developed between the centrosomes outside 
the nucleus and coming later into close connection with it. Only in 
the first division of the promycelium in G. clavariaefornie were 
chromosomes to be observed. The chromosomes were numerous ; 
the two chromosomes observed regularly by Sapin-Trouffy and Maire, 
on which they base their evidence for reduction, represent groups of 
chromosomes or merely chromatin masses. 
These conclusions as to the nature of the fusion in the teleu¬ 
tospore apply equally to the fusion of nuclei in the basidium, for it 
has lately been shown by Maire that the Basidioniycetes also 
have paired nuclei and that, as in the Uredineae, it is the two 
