Ii8 
ALBAN STEWART 
or at least not to the same extent as are the multiseriate rays. Many 
uniseriate rays occur in the xylem of infected areas but the multiseriate 
rays are all much broader than they are in normal wood. It seems 
probable that when the stimulating effect of the fungus reaches a 
given area the cambium in that locality only produces an abnormal 
amount of ray tissue opposite the multiseriate rays. 
From the above figures it can be seen that those portions of the 
infected xylem which are included in the knot are made up of a ray 
tissue to a considerable extent. Farlow (3, p. 446) evidently saw the 
ray-like character of the cells in the knot but did not recognize their 
full significance as he says: ''In the knot we find bast fibers, wood 
cells, and dotted ducts; but the prevailing tissue consists of dotted, 
rectangular, parenchymatous cells, with very thick walls, which 
closely resemble the cells of the medullary rays." 
At the beginning of the second season the growth of the knot is 
very rapid. The small segments of summer wood, formed just inside 
the cambium at the end of the previous seasons growth, are pushed 
outward by the growth of the parenchyma cells and the cells of the 
broad rays. This growth is due largely to an increase in size of both 
parenchyma and ray cells, but whether or not it might also be partly 
due to cell division was not definitely determined. None of these 
cells are in process of division in any of the sections examined, but a 
few instances were found in which a cell appeared to have two nuclei. 
Some of the nuclei were found to be slightly constricted at the center, 
a fact which suggests the possibility of amitosis in these particular 
cells. 
The small segments of summer wood which were formed at the 
end of the previous season's growth, are pushed outward by the growth 
of the surrounding .cells. The radial segments of xylem, such as are 
shown in fig. 8, are torn away from the rest of the xylem to which they 
were connected, and are pushed outward in a similar manner. One 
may often find instances where this is just beginning to take place 
and the gap of separation is but slight. These segments may become 
more or less broken up as they are pushed outward, so that fragments 
of them can be seen scattered around through the parenchyma of the 
knot. Their position is often such as to leave no doubt about their 
origin. In this pushing out of the radial segments of xylem and the 
isolated segments of summer wood, the cambium is also pushed out- 
ward, so it comes to lie much farther away from the center of the stem 
