TISSUE INVASION BY PLASMODIOPHORA BRASSICAE 
By L. O. Kunkei, 
Pathologist, Cotton, Truck, and Forage Crop Disease Investigations, Bureau of Plant 
Industry, United States Department of Agriculture 
INTRODUCTION 
Though many workers have studied the clubroot of crucifers, no 
adequate account has yet been given of the method of infection or of 
the way in which the parasite becomes distributed in the tissues of its 
host. The writer has described in detail in a previous publication 
(9) 1 the manner by which a closely related parasite, Spongospora 
subterranea (Wallroth) Johnson, invades the tissues of the potato 
(,Solatium tuberosum L-). He has also suggested that a similar kind 
of infection may hold for Plasmodiophora brassicae Wor. and other 
members of the Plasmodiophoraceae. With this suggestion in mind a 
study has been made of the clubroot, and it is the chief object of the 
present paper to give data that seems to make clear the method of 
tissue invasion. 
The occurrence of the parasite within the cells of its host is sufficient 
proof that it in some way penetrates cell walls. But we would like to 
know how and when these penetrations take place and the exact method 
by which the large overgrowth arises. Is the slime mold that produces 
the great “clubs” with which we are so familiar able to penetrate only 
the very young rootlets; or is it also capable of attacking older tissues ? 
Does it become distributed by many successive divisions of a few cells 
originally infected; or is there'some other method by which it spreads? 
Do the many groups of infected cells, the so-called “ Krankheitsherde,” 
that are distributed throughout the tissues of a single club result from 
one infection; or is each group the result of a separate infection? What 
is the relation of the parasite to the host tissues, and by what means 
does it injure the host plant? These are some of the questions that 
have not been satisfactorily answered by the students who have already 
contributed so much to our knowledge of other phases of this interesting 
disease. 
Woronin (16) observed amebae which he believed to belong to 
Plasmodiophora brassicae in the root hairs of young plants and assumed 
that they would be able to pass deeper into the young root. Favorski 
(4) believes that infection takes place through the ordinary epidermal 
1 Reference is made by number (italic) to " literature cited,” p. 571-572. 
Journal of Agricultural Research, 
Washington, D. C. 
Pj 
(543) 
Vol. XIV, No. xa 
Sept. 16,1918 
Key No. G-155 
