228 Schwartz. — The Plasmodiophoraceae and their 
members of this family are characterized by a vegetative stage, in which the 
nuclei of the amoebae divide by a process that has been described by Maire 
and Tison as ‘ an intranuclear karyokinesis combined with an amitosis’, and 
by a reproductive stage which closes with two karyokinetic nuclear divisions 
leading to spore formation. 
The family includes the following seven genera : 
1. Plasmodiophora , with free spores. 
2 . Sorosphaera, with spores collected into hollow spheres. 
3 . Tetramyxa , with spores in tetrads. 
4 . Sorodiscus , with spores collected into hollow, flattened spheres and 
ellipsoids. 
5 . Molliardia , with spores at present unknown, 
6 . Spongospora , with spores collected into spongy masses. 
7 . Ligniera, , with spores collected into masses of varying shapes (e. g. 
spheres and ellipsoids). 
Of these genera, the first five possess certain common characteristics in 
that they each contain only a single species, the presence of which in the 
host-plant always gives rise to hypertrophy of tissue with the formation of 
tumours or swellings either in the stem, leaf, inflorescence, or root. The 
genus Spongospora , represented by 5. subterranean causes no apparent 
hypertrophy to the tissues of the potato, on which it is parasitic. 
The genus Plasmodiophora, Wor. 
The cytology of P. Brassicae has been fully described by Nawaschin (16), 
Prowazek (23), and Maire and Tison (11). The statement made by Marchand, 
and quoted by me in my paper on 5. Graminis (25), to the effect that the roots 
of Celery, Sorrel, and Melon had been attacked by this species, has been 
found by Griffon and Maublanc (2) to be an error. Nawaschin states that 
the groups of diseased cells are formed by the division of single or small 
groups of infected cells at the growing apices of the roots, and that the 
amoebae have no power to pass from cell to cell by penetration of the cell- 
wall ; this appears to me to be the case in all the genera. The spores are 
said to germinate readily, but I do not find this to be the case. Although 
I have tried to germinate spores of various ages, including some which had 
been kept through the winter, in no case have I seen an actual germination. 
In cultures of the spores I have occasionally seen a number of small, 
pear-shaped flagellate bodies, but these may very probably have been due 
to other organisms, as the culture was not pure. Prowazek has described 
a karyogamy taking place on spore formation ; this, however, has not been 
confirmed. 
