795 
Sorosphaera Graminis. 
live, each stage being characterized by its nuclei. In Sorosphaera Graminis , 
which I have found considerably better for the observation of the nuclear 
changes than S. Junci , these two stages are well marked. The nucleus in 
the vegetative stage usually consists of a central mass of chromatin, the 
nucleolus or karyosome, situated at the centre of a small, spherical, clear 
space, the whole being surrounded by a delicate nuclear membrane. At 
times, more especially prior to nuclear division, granules of chromatin are 
to be seen on the inner side of this membrane. The nucleus stains well 
with Benda’s iron haematoxylin. The first stage in the division of the 
vegetative nucleus consists in its becoming somewhat elliptical in shape, the 
karyosome elongates, and the chromatin granules collect together to form 
an equatorial plate, the whole giving the appearance of a cruciform structure, 
as shown in Fig. 8, and exactly similar to the corresponding phase that 
has been observed in other Plasmodiophoraceae. The next step consists in 
the splitting of this plate and the passage of the halved portions* one to 
each end of the elongated karyosome to form the ‘dumb-bell ’ or ‘double¬ 
anchor ’ stage shown in Fig. 7, which is similar to that of .S'. Veronicae. 
I have been fortunate in finding a nuclear division showing the actual 
splitting of the equatorial plate, which is drawn in Fig. 6 ; this phase I have 
never actually observed either in S. Veronicae or S. Junci . It appears, 
however, to be somewhat abnormal, as the karyosome is larger and more 
compact and not so elongated as I have usually observed it to be in the 
4 cruciform 5 stage prior to the actual splitting taking place ; it seems probable 
that the equatorial plate has split just before the complete elongation of the 
karyosome. The completion of the nuclear division after the formation of 
the 4 dumb-bell ’ is precisely like that in other Sorosphaerae, the elongated 
karyosome becoming more slender and at length disappearing, whilst the 
nuclear membrane of the two daughter nuclei is completed by the forma¬ 
tion of a new equatorial portion. Figs. 7, 8, 9, and 19 show these various 
stages. 
In the vegetative phase the organism increases in size by the division 
of its nuclei as described above, and may completely fill the root-cell in 
which it is found. On the other hand, many of the cells contain one or 
more irregular amoeboid bodies which at times give rise to daughter 
amoebae by a process of constriction—the so-called schizogony. As is the 
case in the other members of the Plasmodiophoraceae, all the nuclei of 
a given amoebae divide simultaneously, so that they are all to be seen in 
the same phase of the division, as is shown in Fig. 8. 
At the close of the vegetative stage the karyosome gradually decreases 
in size, its chromatin being apparently passed out into the surrounding 
cytoplasm, so that we get a mass of protoplasm with a number of more or 
less spherical vacuoles in the place of the previous nuclei. In these vacuoles 
apparently fresh nuclei are formed, and the organism enters into its repro- 
