556 
Journal of Agricultural Research 
Vol. XIV f No. IS 
that plasmodia which have grown to be large and are heavily charged 
with oil are able to leave the cells in which they live. Such plasmodia 
have never been found penetrating cell walls. 
In the above description of cell-wall penetrations the multinucleate 
masses of parasitic protoplasm have been called “plasmodia.” These 
masses might be looked on by some as multinucleate amebae. It is usually 
considered that plasmodia arise through the fusion of many separate 
amebse rather than by the growth of a single ameba into a large multi¬ 
nucleate mass. In the saprophytic Myxomycetes this point does not 
present difficulties because nuclear division in the ameba is closely 
followed by cell division. In P. brassicae nuclear divisions take place 
without corresponding divisions of the ameboid protoplast. The result 
is that uninucleate amebae may grow into large multinucleate masses 
which can not be distinguished in any way from plasmodia that arise 
through fusion. Tor this reason the writer prefers, for the present at 
least, to designate all multinucleate masses as plasmodia. It should be 
kept clearly in mind, however, that the term is used here solely for 
describing the multinucleate masses seen within the cabbage cells, and 
does not refer to their mode of origin. 
As has already been stated, uninucleate protoplasts have occasionally 
been observed within some of the outer layers of cortical cells. If no 
swelling has yet occurred on the stem, it is probable that such amebse 
have come directly from spores and represent a very early stage of in¬ 
fection. If considerable swelling has already taken place, it is more 
probable that they have arisen by division from a plasmodium. These 
uninucleate masses have been observed in cells of the cambium far re¬ 
moved from the point of original infection. They have also been seen 
in the growing tip of infected stems. Therefore they do not necessarily 
represent recent infection. Plate 70, K, L, M, shows small ameboid 
protoplasts that were observed in cells of the cambium of a plant that 
had been diseased for approximately six weeks. The one is uninucleate, 
the other binucleate, and the third contains four nuclei. They are the 
bodies that continue to spread the disease—namely, the infecting 
amebae and plasmodia. Plate 70, N, shows a cambium cell containing 
several small plasmodia. Three of these are binucleate. The host nucleus 
is shown in process of division. From the distribution of the plasmodia 
in the host protoplasm it would seem that cell division might leave four 
of the plasmodia in one of the daughter cells and only one in the other. 
PRODUCTION OF BRANCH ROOTS AND SHOOTS 
The distortion of dubs by branch roots has already been mentioned. 
In fact, the disease seems to stimulate branching. The secondary roots 
coming from a diseased root may in some instances reach a length of 
several inches, but they are usually much shorter than this. Sometimes 
they are so modified that they never get to be anything more than short 
