236 Schwartz . — The Plasmodiophoraceae and their 
ripening from the outside inwards. Thus the innermost part of the young 
sporangium is plasmodial with nuclei having well-marked karyosomes ; 
contiguous to this region is a narrow belt containing nuclei in which the 
karyosomes are replaced by granules of chromatin, and in the outer portion 
of this belt the plasma becomes discrete, and beyond this point is replaced 
by spores, as may be seen in Figs. 14 and 15. A slightly earlier stage of 
development to that just described is to be seen in Fig. 16, in which the 
karyokinetic nuclear divisions, which precede the spore formation, are to 
be observed in place of the spores. Among these dividing nuclei some are 
to be seen in the ‘ synapsis ’ stage ; these are shown in Fig. 20. 
In Spumaria alba and Arcyria albida I have observed the enlarged and 
degenerate nuclei described by Helene Kranzlin, but have not seen them 
approaching in pairs, nor have I seen any nuclear fusions. 
In Comatricha obtnsata I find that a karyokinetic nuclear division 
takes place within the spore, so that the ripe spore is usually binucleate. 
This division, which is not, however, quite universal, is shown in Fig. 18. 
Comparison of the Plasmodiophoraceae and Mycetozoa. 
In the vegetative stage of the Plasmodiophoraceae we get the well- 
known intranuclear { cruciform ’ type of nuclear division. This is altogether 
lacking in the Mycetozoa, where nothing resembling it has been observed. 
In the vegetative or plasmodial stage of the Mycetozoa Jahn has observed 
typical karyokinetic figures ; Lister also has observed karyokinesis in the 
plasmodium of Badhamia utricular is, although he inclines to the opinion 
that direct nuclear division is the usual form. The akaryote stage which 
follows the vegetative stage in the Plasmodiophoraceae is also wanting in 
the Mycetozoa. These considerations seem to me of sufficient importance 
to justify the separation of the Plasmodiophoraceae from the Mycetozoa. 
Osborn laid stress on the karyogamy observed by him in Spongospora , 
and, on the strength of its similarity to that described by Jahn and Kranzlin 
in the Mycetozoa, considered these processes as homologous and as 
evidence of close relationship. Since, however, Jahn has retracted his 
view, the existence of a karyogamy in the Mycetozoa becomes, to say the 
least, doubtful, and the argument used by Osborn has little weight. Jahn, 
however, as I stated above, also observed a karyogamy or conjugation of 
the nuclei of the young uninucleate amoebae developed from the swarm- 
cells. If, as is possible, a conjugation of the myxamoebae be found in the 
Plasmodiophoraceae, this would furnish evidence of relationship between 
this family and the Mycetozoa. 
The Chytrideae. 
Nemec ( 17 ) has described, in Sorolpidium Betae , a member of this 
family which is quite evidently closely allied to the Plasmodiophoraceae. 
