Nuclear Migrations in Phragmidium violaceum. 
BY 
E. J. WELSFORD, F.L.S., 
Assistant in Department of Plant Physiology and Pathology , Imperial College of Science 
and Technology. 
With Plate XVI. 
D URING the last ten years much work has been done on the life- 
history of the Uredineae, and it has brought to light the fact that the 
development of the aecidiospores is initiated by the formation of binucleated 
cells at the base of the aecidium. 
Blackman (l), 1 in 1904, was the first to show how this took place. He 
found that in Phragmidium violaceum the binucleate condition originated 
in the ‘ fertile cell 5 of the aecidium, and was the result of the migration into 
it of the nucleus of a neighbouring cell. He considered this to be a case of 
reduced fertilization, in which a vegetative cell takes the place of a normal 
male cell. He regarded the spermatia as male cells which had become 
functionless, and suggested that the sterile terminal cell might represent 
an abortive trichogyne. 
In 1905 Christman ( 3 ) investigated the aecidial development of 
Phragmidium speciosum. He found that in this form the binucleate con¬ 
dition is brought about by the gradual breaking down of the walls separating 
two adjacent fertile cells, so that they fuse and eventually give rise to a row 
of binucleate aecidiospores. He considered this to be a conjugation of two 
equal gametes. The spermatia he regarded as gametophytic conidia. This 
type of fertilization was later interpreted by Blackman and Fraser ( 2 ) as 
a case of reduced fertilization in which two female cells associate. This 
second type of fertilization is thus brought into line with the earlier one 
found in Phragmidium violaceum. 
Since this time a large number of forms have been investigated, and it 
has been shown in the majority of cases that fertilization takes place by the 
union of two similar cells. Such a mode of origin of the binucleate 
condition has been described for Phragmidium speciosum ( 3 ), Melampsora 
Rostrupi ( 5 ), Phragmidium potentillae canadensis ( 5 ), Caeoma nitens (12 and 
13 ), Triphragmium Ulmariae ( 13 ), Puccinia transformans ( 13 ), Puccinia 
1 The numbers refer to the list of papers given at the end. 
[Annals of Botany, Vol. XXIX. No. CXIV. April, 1915.] 
