Generations , and General Cytology of the Uredineae . 325 
which shows no signs of specialization as a female reproductive cell, and one 
in which the ancestors of the fusing nuclei have been associated together in 
the same cell for many thousands of generations, lacks all of the characters 
of a sexual process except that of mere nuclear fusion. 
It would, in fact, seem obvious that the critical point for investigation 
in relation to the question of sexuality is the early development of the 
aecidium, for it is there, in the full life-cycle, that the two nuclei first 
become associated, and the transition from the single to the paired con- 
dition takes place. Sapin-Trouffy, however, imbued with the idea of the 
importance of the fusion in the teleutospore, paid little attention to this 
point, but merely states that from the mycelium with single nuclei, binucleate 
hyphae grow up which cut off a series of binucleate aecidiospore-mother- 
cells, from which by division the binucleate aecidiospores are derived. 
The other results obtained by this worker, such as those on the details 
of nuclear division (in which he describes the regular presence of two 
chromosomes and the absence of a spindle) and on chromosome-reduction, 
left much to be desired, owing to the insufficiency of the methods employed. 
The figures which he gives are also of a very diagrammatic nature. In spite, 
however, of the obvious need of further work, the only later contributions of 
importance are those of Maire (29, 30), published in part after this work 
was in progress. Maire accepts the results of Sapin-Trouffy, but states 
that the cells of the aecidium which give origin to the aecidiospore-mother- 
cells are, in Endophyllum Sempervivi , De Bary, and in Puccinia Bunii , DC., 
at first uninucleate, but later become binucleate by a process which he 
believes to be one of simple division. 
The result of cytological observations, as far as they go, is thus to 
suggest that the Uredineae are totally wanting in any ordinary form of 
sexuality or of sexual organs, and that the aecidiospores are produced 
by a structure of the nature of a conidiophore, in which, however, a peculiar 
association of nuclei takes place. The spermatia, however, still remain 
as very puzzling structures on which these investigations throw no light, 
for they are apparently completely wanting in function. 
It is interesting to note that during last year Arthur (1), while admit- 
ting our ignorance of the question of sexuality in the group, has put forward 
the view that the aecidium is ‘ a device to restore vigour to the fungus/ as 
after this stage the parasite usually spreads and develops very rapidly ; the 
sexual nature of the aecidium is thus suggested on physiological grounds. 
An investigation for the purpose of studying the vexed question of 
sexuality and for settling some of the points left doubtful by Sapin- 
Trouffy had been projected ever since the appearance of Sapin-T rouffy ’s 
work, and was carried out during the last two years. It was clear that 
what was required was not so much a rapid survey of the whole group, 
as had been done by Sapin-Trouffy, but the careful investigation of a few 
A a 2 , 
