81 
internally or externally from the sound tissue. In the later stages 
there is a change from pearly white to a yellowish brown. Instead of 
a smooth convex outline the surface is full of fissures, secondary fungi 
gain access, decomposition begins, and the foul odor arises which is so 
characteristic of the disease. These appearances are especially notice¬ 
able in the turnip. (Plate xv, Fig. 3.) 
In the study of the minute anatomy use was made of freehand sec¬ 
tions. Serial sections were also used to a considerable extent, the 
material being embedded in celloidin and cut with the microtome. Sec¬ 
tions through stem and leaf show no trace of any parasite. If a trans¬ 
verse section of one of the spindle-like swellings of the cabbage be cut 
along the line n, b (Plate xv, Fig. 4), where the hypertrophy is least 
marked, and examined with a low power, a more or less mottled ap¬ 
pearance is seen (Plate xv, Fig. 5). This is due to the presence of the 
parasite Plasmodiophora brassicce , Wor. 37 , which is undoubtedly the 
principal cause of the club-root disease. A very noticeable feature is 
that, in general, this appearance is found in the vicinity of the cambium 
c and tracheae tr of the axial portion. Examination with a higher 
power shows this mottled appearance to be due to the presence of mi¬ 
nute spherical bodies, which are so densely packed that the entire lumen 
of the cell is filled. Sections of the turnip along the line a b (Plate xv, 
Fig. 6) show different stages in the development of the Myxomycete. 
There is often found in the same section all the transitional stages be¬ 
tween the plasmodium and mature spores (Plate xv, Fig. 6 a a, b , c). 
The individual cells of the thin-walled parenchyma undergo a marked 
hypertrophy. This is shown by comparing Figs. 7 and 8. The draw¬ 
ings are made from the same section taken along the line c d of 
Fig. 0, Plate xv. Fig. 7 shows the normal tissue of the cambium 
zone taken from the right side, while Fig. 8 shows the pathological 
condition as it occurs on the opposite side. If the peripheral layers 
a be made to coincide, a comparison is readily made. Moreover, 
this swelling is noticed in cells surrounding those infected and where 
no trace of the parasite could be found. Yet this is not sufficient to 
account for the enormous tubercles shown in Plate xv, Figs. 1 and 2. 
This would seem to justify Woronin’s 37 statement that the swellings 
are not only caused through the hypertrophy of individual cells, but 
also by an increase through cell division. The tracheae apparently un¬ 
dergo no changes. Plate xvi, Fig. 9, taken from a section along the line 
a b of Fig. 10 shows one of the vessels more highly magnified. It is 
completely filled with the plasmodium, while the surrounding tissue is 
free from any trace of disease. This at once suggests that the para¬ 
site may thus be readily carried to different parts of the tissue. If now 
the contents of the cells of the medullary rays be examined they are 
found, in the normal tissue, to be loaded with starch. Comparing the 
pathological tissue from the same region a marked change is noticed. 
Instead of the small cells well stored with reserve food, we have the 
