234 Schwartz . — The Plasmodiophoraceae and their 
species, and to some extent they resemble those of Spongospora. The 
spores are very rarely collected into spheres or ellipsoids, which are the 
forms commonly met with in other species. The individual spores are 
approximately of the same size as those of Spongospora. 
The life-history and cytology of the various members of the Plasmodio- 
phoraceae is remarkably uniform, except for the case of M. Triglochinis , in 
which, apparently, there is no spore formation by the parasite in the host- 
plant. With regard to the karyogamy described by Osborn as taking place 
in Spongospora , this has not been observed in any of the other genera. 
I have re-examined my slides of 5 . Veronicae with a view of confirming 
Osborn’s observation, but have found no such karyogamy as he describes, 
although this species is a favourable one for the observation of nuclear 
changes, the akaryote and early spore forms being well marked and plentiful. 
It would, I think, be easy to mistake overlapping nuclei or the close of 
a mitosis for a karyogamy. Winge also fails to see any signs of a karyogamy 
in Sorodiscus Callitrichis , which is also a favourable subject for observation. 
Of the karyogamy described by Osborn, Winge remarks : ‘ If a karyogamy 
at this stage is really found in Spongospora , we should rather conclude that 
this organism is not a Plasmodiophoracea.’ Maire and Tison have also 
failed to find a karyogamy in either vS\ Veronicae or the other species studied 
and described by them ; they suggest, as also does Winge, that a conjuga- 
tion of amoebae follows the germination of the spores. This suggestion 
I also made in my paper on .S'. Junci. The refusal of the spores to germi- 
nate under artificial conditions is unfortunate ; probably the germinated 
spore gives rise to a pear-shaped swarm-cell, and it is at this stage that 
a conjugation should be looked for. 
Mycetozoa. 
In 1884 Strasburger observed a simultaneous mitosis of all the nuclei 
in the developing sporangium of Trichia fallax ; this mitosis gives rise to 
the nuclei of the spores. This simultaneous nuclear division has since been 
observed in other species, and is stated by Pavillard ( 21 ) to be probably 
constant throughout the endosporous Mycetozoa. 
In 1907 Jahn and Helene Kranzlin (8) identified this division as 
a heterotypic mitosis ; according to this view, the reduction would be 
completed on the germination of the spore. In Arcyria and Trichia 
Kranzlin states that just prior to spore formation the nuclei in the 
sporangium associate in pairs and a karyogamy takes place, and that any 
nuclei which have not paired quickly degenerate. Kranzlin states further 
that a temporary enlargement of the nucleus follows, and that then 
synapsis takes place. In the exosporous genus Ceratiomyxa a karyogamy 
has been described by Olive ( 19 ) and Jahn (6), but their accounts do not 
agree. 
