Welsford.—Nuclear Migrations in Phragmidium violaceum . 297 
closely allied forms show two very different types of fertilization certainly 
lends support to the view that both are reduced, being derived probably 
from an earlier normal sexual process of fertilization by spermatia. If we agree 
that the peculiar fertilization processes of the aecidium and the existence 
of the spermatia are sufficient evidence that the more primitive sexual 
organs are to be found in the aecidium, then we must assume that this type 
of spore form is the oldest. This is the essential point of Blackman’s view 
as opposed to Christman’s. It is not necessary to assume that the eu-forms 
as they occur at the present day are more primitive than, for example, the 
brachy- or micro-forms. It is possible that these forms were reduced from 
a primitive aecidium-bearing form independently of the eu-forms, by the 
loss of the aecidium and the shifting forwards in the life-history of the 
point of nuclear association. On the other hand, the complex eu-forms 
may have developed independently with further elaboration of the life- 
history, but without loss of the aecidium. 
Summary. 
1. A re-examination of Phragmidium violaceum completely confirms 
Blackman’s observation that fertilization is brought about by the migration 
of a vegetative nucleus to a fertile cell. 
2. No other mode of origin of the binucleate cells was observed. 
3. The size of the pore through which the nucleus passes is very 
variable, sometimes being as much as 3 /x in width. Cells were found in 
which the pore was visible after the nucleus had migrated through it. 
4. A layer of more or less empty cells occurs immediately below the 
binucleate fertile cells, and is made up of those cells from which the nuclei 
have migrated. 
5. That the nuclear migrations are not pathological in nature is shown 
by the facts that : 
(i) They occur in regular sequence from the middle to the periphery 
of the aecidium. 
(ii) They are not found in the paraphyses at the periphery of the 
aecidia where the cells are nearer to the wounded surface. 
(iii) They are found in material fixed in various ways. 
It is with great pleasure that I record my thanks to Professor Blackman 
for his valuable help and criticism. 
List of References. 
1 . Blackman, V. H. : On the Fertilization, Alternation of Generations, and General Cytology of 
the Uredineae. Ann. of Bot., vol. xviii, J904. 
2 . -and Fraser, H. C. I.: Further Studies on the Sexuality of the Uredineae. 
Ann. of Bot., vol. xx, 1906. 
