Relationship to the Mycetozoa and the Chytrideae . 237 
Among the points of resemblance between them may be mentioned the fact 
that Sorolpidium possesses two distinct forms of nuclei — -viz. vegetative nuclei 
in which the chromatin is collected into a central karyosome, and repro- 
ductive nuclei in which the karyosomes are lacking. The resemblance is 
rendered the more evident by the mode of division of the vegetative nuclei 
which Nemec states is by an amitotic division of the karyosome combined 
with an equatorial plate of idiochromatin. In the Plasmodiophoraceae the 
spores are, however, formed after two karyokinetic divisions, whereas in 
Sorolpidium the spore mother-cells form the resting stage, and later each 
cell nucleus undergoes two karyokineses, thus giving rise to four zoospores. 
The amoeboid vegetative stage in Sorolpidium is succeeded by the repro- 
ductive phase in which the organism divides into a number of uninucleate 
myxamoebae which form the spore mother-cells which are contained in 
a sporangium with an enclosing wall. Thus in the Plasmodiophoraceae we 
get clusters of spores, each spore of which is, in most genera, formed from 
a uninucleate amoeba ; these clusters are usually enclosed by a common 
membrane, and constitute the resting stage of the organism. For the rest- 
ing stage in Sorolpidium we get collections of spore mother- cells, each cell 
of which is formed from a uninucleate amoeba ; these collections are enclosed 
in a membrane, and each spore mother-cell produces four zoospores. 
Kusano ( 9 ) has also described a species of Olpidium parasitic on Vicia 
unijuga . He states that in the amoeboid vegetative stage the nuclei, which 
contain a prominent karyosome, divide amitotically, there being, however, 
no plate of idiochromatin as in the previous species. Later on the nuclei 
lose their karyosomes and become reproductive nuclei. These, like the 
corresponding ones in the Plasmodiophoraceae, undergo karyokinetic divi- 
sions, but give rise to the mother-cells of the zoospores. The zoospores 
conjugate in pairs, and the zygote gives rise to resting sporangia, which at 
first are binucleate, fusion of the nuclei taking place later. During the 
development of the resting sporangia the nuclei pass through a phase 
similar to the akaryote stage in the Plasmodiophoraceae. 
I have observed in some few of the roots of Mentha Pidegium the 
presence of an Olpidium similar to those described above, but on account 
of inability to obtain sufficient material I have been unable to cover 
completely its life-history. This Olpidium is found in the cells in the form 
of amoebae of varying size, which apparently fuse to form a plasmodium. 
These amoebae differ from those of the Ligniera in being much larger, 
in having power of penetrating the cell-walls, and in their nuclei being much 
smaller ; also they are not found in groups as are those of the Ligniera , and 
they are usually seen in the neighbourhood of the sporangia to which they 
give rise. The sporangium, which is surrounded by a membrane, contains 
the reproductive nuclei which probably give rise to the zoospores. This 
organism is shown in Figs. 21 and 22, 
