296 Welsford.—Nuclear Migrations in Phragmidium violaceum . 
that, from analogy with other groups, the gametophyte generation should 
be the primitive generation, and therefore that those forms with the simplest 
sporophyte generation—that is to say, the lepto- and micro-forms—are the 
most primitive. He regards the various types of spores as homologous, and 
considers that in the lepto- and micro-group the gametophyte bears the 
gametes and produces the fusion cell. The point at which the cell fusions 
occur has receded further and further from the teleutospore, the sporophyte 
generation becoming more elaborate, till, in the higher groups, an aecidium 
has been introduced and the eu-forms appear. The ‘ fusion cell ’ he regards 
as the product of two isogametes which have formed a zygospore like that 
of the moulds, but, unlike them, has no resting stage and produces many 
spores. The spermatia he regards as gametophytic conidia. 
The main objections to this view are ( 1 ) that it ignores the phenomena 
described for Phragmidium violaceum , assuming that they are due to some 
pathological cause, and (2) that it offers no adequate explanation of the 
spermatia. 
The observations recorded in this paper show the untenability of the 
view that nuclear migrations in the aecidium of Phragmidium violaceitm 
are pathological in nature. Also one would hardly expect to find conidia 
which are apparently functionless produced at the same time as the very 
effective aecidiospores; and, as has been pointed out by Blackman, the relative 
proportion of nucleus and cytoplasm exhibited by the spermatia is quite out 
of keeping with what is known of conidia. 
The alternative hypothesis is that put forward by Blackman in 1904. 
He regards the Uredineae as a group in which a great variety of reduced 
forms occur. He considers that they are derived from an ancestor with 
a typical sexual process, the male cells being now represented by the 
spermatia and the female by the * fertile cells ’; these latter were provided 
with a trichogyne which now possibly exists as a ‘ sterile ’ or ‘ buffer 5 cell. 
According to this interpretation, all these Uredineae which have at present 
been investigated have a reduced type of fertilization, Phragmidium 
violaceum being fertilized by a vegetative instead of a male cell, whilst in 
Phragmidium speciosum reduced fertilization is effected by means of female 
cells. The two types of fusion found in the Uredineae are thus considered 
to be heterogamous instead of isogamous, and the group is regarded as 
showing relationship with the Florideae rather than with the Zygomycetes. 
It is, of course, very difficult to decide between these two views. There 
are at present no data as to whether the heterogamous or isogamous union 
in the aecidium is the more primitive. If the nuclear migrations of Phrag¬ 
midium violaceum are to be looked upon as reduced in comparison with 
the isogamous unions which have been described for so many aecidia, then 
it is still possible to homologize, with Christman, the aecidium and the 
primary uredospore cell. On the other hand, the fact that the Caeomas of 
