a New Genus of P lasmodiophoraceae. 647 
The infected cells grow to an abnormal size (PL XLV, Fig. 4), reaching 
about 135-200 [j, across, the normal ones measuring only 35 /x, and 
their nuclei are dissolved towards the beginning of the sporogonic stage 
(PL XLV, Fig. 3). The mature spores have a brown and rather thick 
membrane, their diameter being about 4/x. The spore masses entirely fill 
every infected cell as in the case of Plasmodiophora (PL XLV, Figs. 3, 4). 
By the pressure of the giant cells the elements of the surrounding outer 
cortex become stretched tangentially (PL XLV, Fig. 4), whereas normally 
they are radially elongated (Text-fig. 2). Unilateral attacks may occur, the 
central cylinder thereby being laterally displaced— -in extreme cases almost 
Text-fig. 4. Part of a median longitudinal section just under the growing apex of an infected 
Diplanthera stem, a , the central cylinder ; b, the inner cortex ; c, the outer cortex ; d, the epi- 
dermis. The nuclei of the host plant are shaded. Uninucleate amoebae of Ostenfeldiello (repre- 
sented by small circles) are seen only in the cells of the inner cortex, x 300. 
to the periphery of the stem. As a rule the diameter of the infected inter- 
nodes is enlarged to two to three times that of the normal ones, these latter 
being commonly about 1 mm. across. 
The above-mentioned characteristic localization of our fungus in the 
tissues of Diplanthera Wrightii explains the fact that an infected stem can 
keep on growing in spite of the parasite. The central cylinder, as well as 
the outer cortex, escapes the attack ; hence the transport of nourishment, 
assimilation, and respiration are not disturbed by the parasite. 
The common picture of the attack, we suppose, must be painted as 
follows : Zoospores are swarming in the mud and penetrate the young apex 
of a Diplanthera stem, until the initials of the inner cortex are reached. 
