364 Blackman . — On the Fertilization , Alternation of 
the migration into it of the nucleus of one of the undifferentiated mycelial 
cells at its base. It then undergoes a series of rapid divisions, cutting off 
a series of aecidiospore-mother-cells. The ‘ fertile cell 5 has thus the 
characters of a female cell. 
The aecidium of Phrag. violaceum is to be considered as a sorus of 
female reproductive organs , each of which consists of a sterile cell above 
and a female cell below, the nucleus of an ordinary vegetative cell bringing 
about fertilization and performing the part which was apparently formerly 
taken by the nucleus of the spermatium. The female cell thus develops 
by means of a reduced form of fertilization. 
It is suggested that the sterile cell is reduced, and that it formerly 
pushed its way to the surface (as it can sometimes now be observed to 
do) and acted as a trichogyne to bring the spermatium into relation with the 
female cell below. 
In the process of fertilization the two nuclei do not fuse, but merely 
remain very closely associated (as in the egg of Cyclops) ; there is thus 
started in the female cell the condition of paired nuclei which continues up 
to the teleutospore. 
The aecidium throughout the group must be considered as a sorus of 
reduced female reproductive organs , for it appears to be always the fertile 
cell which becomes binucleate. Whether in all cases there is a nuclear 
migration, or whether in some there is a still further reduction and the 
process consists of an association of two daughter-nuclei, has yet to be deter- 
mined, as has also the question of the presence or absence of a sterile cell. 
As the spermogonia and aecidia are to be considered as male and 
female reproductive organs, respectively, it is evident that the Uredineae 
which possess an aecidial stage in their life-history ( eu - and -opsis forms) 
exhibit a well-marked alternation of generations which are not only to be 
distinguished as sexual and asexual, but are also to be sharply differentiated 
cytologically, the sexual generation being characterized by single nuclei (with 
two chromatin masses on division), the asexual by paired nuclei (with four 
chromatin masses on division). The transition from the gametophyte to the 
sporophy te takes place in the aecidium and the transition from the sporophyte 
to the gametophyte in the teleutospore. The alternation of generations is 
thus as clearly marked as that of the higher plants or of the Dictyotaceae. 
The fusion in the teleutospore of the two nuclei— the direct descendants 
of those which first became associated in the fertile ( female ) cell of the 
aecidium — is clearly not in itself a process of fertilization (nor the teleuto- 
spore an egg-cell), as Dangeard and Sapin-Trouffy supposed, but a mere 
secondary process, the result of fertilization and the preliminary to reduction. 
It is pointed out that three nuclear stages are to be observed in the sexual 
cycle of plants and animals — nuclear association , nuclear reduction (so-called 
fusion)) and chromosome-reduction. Of these three stages, only the first 
