Osborn . — Sfiongospora subterranea , ( Wallroth ) Johnson. 337 
a simultaneous division of all the nuclei occurs, which, on the ground of 
the prophases, is regarded as heterotypic. This first division is immediately 
followed by spore formation. c Le processus de reduction se trouve ainsi 
interrompu, pendant toute la periode de la vie ralentie de la spore mure. 
La reduction s’acheve a la germination,’ 1 the succeeding homotypic division 
being the one described by Jahn 2 in the swarm spore. 
In the exosporous genus, Ceratiomyxa , Olive 3 and Jahn 4 have described 
a karyogamy. This occurs, according to Olive, towards the close of the 
segmentation of the protoplasm, and is followed by synapsis, each potential 
spore mass receiving a nucleus in that state. Two divisions follow, giving 
the typical four-nucleate spore. 
Jahn’s account is quite different. Following nuclear fusion, which he 
places at an earlier stage, there are stages regarded by him as synapsis and 
diakinesis, though it is to be regretted that his figures of the latter are 
not more convincing. There is, then, one (heterotypic) division of the 
nucleus, followed by a degeneration of half the daughter nuclei. The 
remaining nuclei form the spores, in which a double karyokinesis occurs. 
Yet another nuclear division takes place on germination, so that eight 
swarm spores are freed. It is not easy to homologize this account with 
what is known of the endosporous genera. Jahn regards the nuclear reduc- 
tion as completed by the heterotype division and the subsequent nuclear 
degeneration, the two divisions in the spore, and that on its germination 
as of no special significance. In his review of the work, Pavillard 5 suggests 
that probably the division on the germination of the spore is a true homo- 
typical mitosis (comparable to that in the Endosporae)> the two preceding 
divisions being ordinary mitoses interpolated between the heterotype and 
the homotype divisions, and of no special significance. 
Discussion and conclusions. The formation of a definite plasmodium 
has been described in the life-history of Spongospora. Prior to spore forma- 
tion the host cell is found to contain a large multinucleate mass of proto- 
plasm in the place of separate amoebae. All the nuclei in each mass divide 
at the same time, and the spores resulting from these divisions are united 
as a rule in a single spore ball. 
The question of the formation of a true plasmodium in Plasmodio- 
phora is the subject of a disagreement among the various workers on 
the organism. In Sorosphaeva there is stated to be no plasmodium 
formation. 
If these three genera are to be united, either in the Plasmodiophoraceae 
according to Maire and Tison, or in the Sorophoreae of Schroter, the defini- 
1 Pavillard, J. : loc. cit., p. 510. 
2 Jahn, E. : Ber. d. deutsch. bot. Gesell., vol. xxii, 1904, p. 84. 
3 Olive, E. W. : Trans. Wiscon. Acad, of Arts, Sci. and Litt., vol. xv, pt. ii, 1907, p. 753. 
* Jahn, E. : loc. cit., vol. xxvi a, 1908, p. 342. 
5 Pavillard, J. : loc. cit., p. 511. 
