546 
Journal of Agricultural Research 
Vol. XIV, No. xa 
They were then washed clean and a small bit of infectious material 
was placed on each a short distance below the earth line. Care was 
always taken to place the infectious material on a portion of the stem 
that was smooth and free of roots. The inoculum was then sealed to 
the stem by means of melted paraffin. Sometimes instead of sealing 
with paraffin it was held in place by wrapping the stem with a small 
cotton string. Inoculated portions of the stem were wrapped in much 
the same way that the nurseryman wraps the stems of budded plants. 
The object was to prevent the inoculum from spreading from the tissue 
to which it was attached, and both methods served the purpose equally 
well. After the infectious material was fixed to the stems the earth 
was replaced and the plants incubated for various periods of time. 
Plate 61 shows a cabbage plant that was treated in the manner just 
described. This particular plant was inoculated when about 2 months 
old. The picture was taken approximately six weeks after inoculation. 
The small roots coming from the club and from the stem above the 
club were not present at the time the plant was inoculated. This 
illustration shows the size of the gall that may result from an original 
infection of a small circular area of tissue not more than 2 mm. in diam¬ 
eter. It will be seen that only the tissues adjacent to the spot where 
the infectious material was sealed are diseased. The fibrous roots are 
all free of disease. Plate 62 shows a portion of two other plants along 
with the plant shown in Plate 61 for comparison. These two clubs are 
smoother than that on the plant shown in the middle. This is because 
fewer branch roots have come from them. The clubs are in general 
outline spindle-shaped, but they are thicker on one side than on the 
other. The thick side is the one to which the inoculum was sealed. 
During the last summer the stems of more than 2,000 plants were 
inoculated. These plants varied in age from 1 month to more than a 
year. Without a single exception they became diseased. Old stems an 
inch or more in diameter became infected almost as readily as young 
ones. 
These experiments bring out two important facts. They show that 
old tissues are readily penetrated by the parasite and that root hairs are 
by no means necessary to infection. In the second place they show 
that the disease spreads from a point of original infection to adjacent 
tissues. 
MORPHOLOGY OF THE CLUB 
The most casual observation of the roots of diseased cabbage plants 
reveals the fact that many of the overgrowths are not the irregular 
swellings that one might expect if they resulted from a large number of 
separate infections by freely moving amebae each independent of all the 
others. Such a fortuitous method of infection might give tumors of 
many different sizes and forms, but it would hardly produce the definite 
