Weisford.—Nuclear Migrations in Phragmidium violaceum. 295 
hypha and passes in laterally (Fig. 2). In no case was a migration found from 
one fertile cell to another. In very young aecidia the migrations were found 
to occur in the middle region of an aecidium, whilst in rather older examples 
cells of this region were already binucleate, and then the migrations were 
found only in the cells immediately outside these. Sometimes the nucleus 
passes through a very small pore in the wall (Figs. 1 and 4), and thus 
becomes greatly constricted (cf. Blackman ( 1 ), Figs. 67, 68). More com¬ 
monly, however, the pore is rather larger, and the nucleus is only slightly 
constricted during its passage and corresponds to Blackman’s Fig. 66 ; such 
cases are shown in PI. XVI, Figs. 2, 3, 5, 6, and 7. In a few cases the hole 
was of considerable size, as shown in Figs. 8 and 9. When it was found 
that the nuclei sometimes pass through a large hole on the cell-wall, it 
seemed unlikely that such holes would be later obliterated, and a careful 
search was made amongst the older binucleate cells, with the result that 
a few cases were observed, and two of these are shown in PI. XVI, 
Figs. 10 and 11. 
The cells from which the nuclei have migrated gradually lose their 
cytoplasm and become almost or quite empty; they form a fairly con¬ 
spicuous layer surrounding the bases of the old fertile cells. PI. XVI, 
Fig. 13, is a semi-diagrammatic drawing of the middle of a young aecidium, 
the fertile cells are binucleate, and below them is the layer of empty cells. 
Part of the same aecidium, but nearer to the periphery, is shown in Fig. 12 
where the fertile cells are as yet uninucleate and have no empty cells at 
their bases. In thick sections of older material the empty cells form a con¬ 
spicuous layer; Fig. 14 is a semi-diagrammatic representation of such 
a preparation, showing the young aecidiospores, the binucleate fertile cells, 
a layer of empty cells, and below that a mass of uninucleate hyphae ramifying 
in the tissue of the host. 
In spite of a careful search, fusion between two fertile cells was never 
observed, but no less than twenty-eight cases of migration of a vegetative 
nucleus into a fertile cell were found. It is also important to note, as stated 
earlier, that in fairly young aecidia the migrations are found to occur only 
in connexion with the cells immediately peripheral to the central mass of 
binucleate fertile cells. This special localization of the ‘ migrations 5 and 
the absence of lateral fusion of fertile cells are in themselves sufficient to 
show that the passage of a vegetative nucleus into a fertile cell is the normal 
method of origin of the binucleate condition in this form. Migrating nuclei 
always pass from a vegetative to a fertile cell, and no cases were found of 
nuclear migrations between fertile cells or between vegetative cells. It may 
be mentioned that the paraphyses towards the periphery of the aecidium 
are often multinucleate, and nuclear divisions occur frequently in them. 
Christman has put forward a very interesting view as to the morphology 
of the aecidium and the phylogeny of the group generally. He points out 
