Further Studies on the Sexuality of the Uredineae. 
BY 
VERNON H. BLACKMAN, M.A., F.L.S., 
Assistant , Department of Botany , British Museum ; Lecturer on Botany , East London College ; 
formerly Fellow of St. John' s College , Cambridge. 
AND 
HELEN C. I. FRASER, B.Sc., F.L.S., 
Assistant Lecturer on Botany , Royal Holloway College. 
With Plates III and IV. 
E ARLIER studies by one of us (1) have shown that in the aecidium 
of Phragmidiuni violaceum a peculiar process occurs, in which the 
nucleus of an ordinary vegetative cell migrates into a special £ fertile 
cell/ which then develops actively and gives origin to a series of binucleate 
aecidiospores and intercalary cells, the two nuclei always dividing by 
a process of conjugate division. This fertile cell was considered to be 
a female cell, and its union with the vegetative cell a ‘ reduced sexual 
process* in which the latter cell replaces the now functionless male 
cell (spermatium). 
These further studies were undertaken to ascertain how far this process 
would explain generally the origin of the conjugate nuclear condition 
which is known to be constant in the cells of the aecidium which produce 
the aecidiospore-rows. The development of the typical aecidium with 
its definite pseudoperidium, and its comparatively deep point of origin 
in the tissues of the host, obviously required cytological investigation 
for comparison with that of Phragmidiuni. For in that genus the aecidium 
(the so-called caeoma) is of very simple type, consisting merely of a single 
layer of fertile cells developed directly beneath the epidermis, and bounded 
only by a few paraphyses ; and even these may sometimes be absent. 
It was also hoped that further investigation might throw some light 
on the cytological life-history of the reduced forms which, possessing no 
aecidium, yet show cells with conjugate nuclei at some stage of develop- 
ment, the paired nuclei fusing sooner or later in the teleutospore. 
While this work was in progress a very interesting paper appeared 
[Annals of Botany, Vol. XX. No. LXXVII. January, 1906.] 
D 2 
