554 
Journal of Agricultural Research 
Vol. XIV, No. 13 
around the stem of a cabbage plant, infection would be general over the 
inoculated surface of the stem. This, however, is not the case. Under 
such circumstances infection starts at a good many different points, 
but it is never general over the entire surface. No evidence has been 
obtained that primary infection takes place through wounds. What 
it is that determines the original point of entrance is a problem that 
remains to be solved. 
PASSAGE OF PLASMODIA THROUGH HOST TISSUES 
As has already been said, both Lutman (jo) and Chupp (2) have de¬ 
scribed and pictured plasmodia in the act of passing from one cell into 
another. Neither of these authors has attempted to show the stages 
by which this process takes place or to describe it in detail. The writer 
has, therefore, made a further study of this phase of the problem. 
In sections of young roots plasmodia were occasionally seen in the act 
of what seemed to be cell-wall penetration. The process was so seldom 
observed, however, that the writer was never quite able to convince 
himself that the appearances met with might not be due to the effect 
of the fixative on the pathological tissues. In the study of the early 
stages of infection, cell-wall penetrations were found so frequently as to 
leave no doubt but that they play a part in normal infection. These 
penetrations were especially abundant around the edges of the small 
infection plugs in material that was killed 13 and 14 days after 
inoculation. Material of this age showed a number of different stages in 
the process of cell wall penetration. A few instances were observed 
where plasmodia were closely applied to cell walls but in which no 
penetration had occurred. Such a case is shown in Plate 70, B. The 
infected cell is somewhat plasmolyzed by the fixative, but the plasmo- 
dium has not been pulled away from the cell wall. The wall, moreover, 
is seen to bend away from the plasmodium as though a pressure were 
being exerted on it by the parasite. Plate 70, C, shows another very 
young plasmodium that has penetrated a cell wall and is beginning to 
pass through it. This plasmodium contains three nuclei. Figure D 
shows a little later stage in the passage of a plasmodium through another 
wall. The parasite has penetrated the wall, but has not yet entered the 
protoplast of the new host cell. Plasmolysis of the two cells by the 
fixative has been an advantage in bringing out this fact. The plasmo¬ 
dium contained so much oil that it was not possible to see the nuclei. 
A still later stage is to be seen in figure E. Here the host cells are not 
plasmolyzed. The plasmodium is well stained and the opening through 
which it is passing is clearly shown. Much the same stage is repre¬ 
sented in figure F. In this figure the parasite is shown passing through 
the end of a cell that lies near the cambium. The stage represented in 
figure G is very interesting because a nucleus is in the act of passing 
through the opening in the cell wall. This is the only instance in which 
