794 Schwartz .— The Life-history and Cytology of 
gated, either through failure in the formation of transverse walls or through 
the absorption of such walls by the parasite. The nuclei of the root-cells, 
when visible, show some hypertrophy and signs of degeneration. In this 
stage, which is shown in PL LXI, Fig. 15, the appearance of the root is very 
similar to that of a diseased Jmiens root. 
In roots in which the disease has reached a more advanced stage, many 
of the cortical cells are filled with the spore collections of the Sorosphaera ; 
the true spherical sorosphere is, however, but rarely to be seen, the most 
usual form being oblong, with slightly rounded ends as shown in Figs. 14 
and 20. Other cortical cells may contain a crowded mass of small mono- 
nucleate amoebae in an incipient stage of spore formation (as seen in 
Fig. 10). The general appearance of such roots is considerably different 
from those of diseased Junci ; the diseased cells, however, are frequently 
to be seen in longitudinal rows as they were in the Juncus root. 
In addition to the probability of infection being effected through the 
agency of eel-worms, the amoebae may obtain an entrance into the root by 
the penetration of a mononucleate amoeba into a root-hair. I have observed 
root-hairs containing amoebae of various sizes, one of which is showm in 
Fig. 7, in which the nuclei are to be seen in the dumb-bell stage of division. 
This mode of infection is similar to what I have observed with Sorosphaera 
Junci , and doubtless it is the usual method by which the members of the 
Plasmodiophoraceae enter their host plant. I have also found root-hairs of 
Zannichellia Palustris serving in similar fashion for the entrance of Tetra- 
myxaparasitica. The root apices probably serve also as points of entrance, 
as they are frequently diseased ; this mode of infection would probably give 
rise to the longitudinal rows of diseased cells at times to be seen in the 
roots. Young branch roots often show the first signs of the presence of 
disease at or near to their apices. 
Cytology of Sorosphaera Graminis. The amoeboid organism varies 
considerably in size from a quite small mononucleated mass of protoplasm, 
as shown in Fig. 5,^, to one of considerable size, as shown in Fig. 15. The 
young amoebae are often pear shaped, and in response to some attraction 
make their way to the nuclei of the plant cells; two such amoebae are 
shown in Fig. 16 with the plant nucleus between them. At times these 
small amoebae fuse together to form a plasmodium, which, after repeated 
nuclear division, will increase in size and finally occupy the whole of the 
root-cell. The smaller amoebae, as shown in Figs. 5 and 15, are very 
irregular in shape, and put out pseudopodia or protoplasmic threads, 
which appear at times to pass through the walls of the cells. I have 
never observed, however, any migration of a nucleus from one cell into 
a neighbouring one. 
The life-history of the parasite may, as in the case of other Plasmodio¬ 
phoraceae, be divided into two stages, viz. the vegetative and the reproduc- 
