544 
Journal of Agricultural Research 
Vol. XIV, No. xa 
cells of very young rootlets rather than through the root hairs. Atkin¬ 
son (i) suggests that the amebae are capable of— 
streaming out in such fine threads as to enter the roots of the cabbage along with 
watery solutions of nutrients, 
while Eycleshymer (3), finding plasmodia in the vessels of fibrovascular 
bundles, thinks that they may be spread in this manner. 
Nawaschin (13) observed that infected cells frequently divide and 
believed that the “ Krankheitsherde” arise in this way from one or more 
originally infected cells. He never saw the passage of the parasite 
from cell to cell and believed that this could not take place after roots 
begin secondary growth. He says that the tissues probably become 
infected while very young but that he was unable to observe stages in 
the process of tissue invasion. 
In a recent paper on clubroot Chupp (2) takes up the problem of 
infection and distribution of the organism in the host tissues. Like 
most other students of the disease, he is of the opinion that only very 
young rootlets bearing root hairs are susceptible and states that, so 
far as his observations go— 
there seems to be no question but that penetration does take place through the root 
hairs and through these only. 
He confirms Lutman (jo) in the observation of actual cell-wall pene¬ 
trations. In describing the behavior of infection amebae, Chupp says: 
They may enter in almost a straight path as far as the endodermis, 
and argues that a single ameba might give rise to from one to probably 
six “ Krankheitsherde” in the primary cortex. He does not describe the 
infection of the stele, which is obviously the important part of the 
problem of tissue invasion. Woronin (16) long ago pointed out that the 
primary cortex of young cabbage roots breaks down and is thrown off 
soon after secondary growth begins. Favorski (4) observed that most 
of the cells infected with Plasmodiophora lie within the central cylinder. 
EXPERIMENTAL METHODS 
The methods that have been used in each part of this work will be 
given at the time the different experiments are described. A few points 
need mention here. Cabbage plants have been used as the host in all 
cases. The plants were grown in pots in a greenhouse for winter work. 
In summer they were grown outside in a garden. Most of the microtome 
sections were cut in thicknesses varying from 5 to 10 ju. A few have 
been cut 20 n thick. Several fixatives were used to kill material, but 
Flemming's solutions proved most satisfactory. All of the sections have 
been stained with Flemming’s triple stain. Nawaschin’s ( 13 ) method 
of leaving sections unbleached so that the oil in the plasmodia, blackened 
by the osmic acid of the fixative, may serve to make the parasite stand 
out sharply from the protoplasm of the host, has been used extensively. 
