Generations , and General Cytology of the Uredineae. 359 
with the aecidium in their life-cycle exhibit an alternation of generations as 
sharply marked as that of the higher plants. For not only are the two 
generations to be distinguished as sexual and asexual — bearing in the one 
case the sexual organs, spermogonia and aecidia, and in the other case only 
asexual spores, aecidiospores, uredospores, and teleutospores — but they 
are also to be cytologically differentiated, the sexual generation being 
characterized by the presence of single nuclei, the asexual by the presence 
of paired (conjugate) nuclei ; the special nuclear condition of the sporophyte 
being the result, as in the case of the 2 n chromosomes of the higher plants, 
of a process of fertilization (at least in Phrag . violaceum). 
Owing to the extreme reduction in the process of nuclear division in 
the Uredineae, so that the process of chromosome-formation is in abeyance 
in nearly all the divisions, one cannot distinguish the two generations by 
their number of chromosomes ; yet one can distinguish in the nuclei of the 
oophyte two chromatin masses, while the two paired nuclei, which together 
correspond with the single nucleus of the ordinary sporophyte, show four 
chromatin masses. There is thus a near approach to the distinction of 
chromosome number which is to be found in the higher plants, and also in 
the interesting alternation of generations which Williams (59, 60) has lately 
observed in the Dictyotaceae. 
The teleutospore clearly corresponds to the spore-mother-cell, for it 
is there that the return to the nuclear condition characteristic of the 
oophyte is brought about. In the teleutospore, although no actual reduc- 
tion of chromosomes can be observed, there is a reduction from the four 
chromatin masses of the two nuclei to the two chromatin masses of the 
single nucleus, each mass, as shown above, appearing to correspond to 
a group of chromosomes. This reduction in number of chromatin masses 
is also associated with peculiar changes in the nucleus concerned which 
correspond to the process of synapsis. 
As however the two nuclei remain individualized from the time of 
fertilization up to the time of reduction in number of chromatin masses we 
have associated with this process a nuclear reduction , i. e. a reduction in the 
number of the nuclei from two to one. Since this process of nuclear 
reduction takes place in most organisms at the time of fertilization, or soon 
after, it has been confused with that process itself, and so has led to the 
belief that the fusion of nuclei in the teleutospore was itself a sexual 
process. This view, which was hardly credible even on the facts hitherto 
known, has been rendered quite untenable by the discovery of an association 
of nuclei in the aecidium, which must itself be considered as the fertilization 
process. 
After the process of synapsis and chromatin-reduction, the cell of the 
teleutospore undergoes a process of tetrad division to form the four cells of the 
‘ promycelium ’( = spores). The teleutospore (or its cell) is thus exactly 
