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ALBAN STEWART 
to be found in this altered position. The cambium may become 
completely broken up in these misplaced segments, resulting in the 
production of isolated xylem cells, or groups of a few of them together, 
scattered around through the cortical portion of the knot. Some- 
times a considerable number of cambium cells may remain together 
and develop the usual elements to which they give rise but in a very 
much altered position. A condition of this kind is shown in fig. 7. 
The outer ends of two adjacent xylem wedges are shown on the 
lower side of the figure, each of which is subtended by a triangular 
shaped mass of phloem cells. These wedges are separated from 
each other by a broad ray, opposite which there is an overturned 
segment of xylem extending straight out into the bark, with the long 
axes of its cells at right angles to their usual position. Uniseriate 
rays occur in this segment but the view presented of them is the one 
usually seen in tangential sections of the wood. A more highly magni- 
fied photograph of the outer portion of this segment is shown in 
fig. 10. 
When the disorganization of the misplaced cambium segments has 
gone still further a condition similar to that shown in fig. ii is com- 
monly found. This photograph was taken from a radial section cut 
through the cortical portion of a mature knot, and shows a band of 
fibers and tracheids extending diagonally across the photograph, which 
assumes an almost vertical direction near the center of the figure. 
Fibers and tracheids maintain this direction for a short distance and 
then bend almost at right angles and extend outward nearly to the stro- 
matic layer shown on the right of the figure. Many of these mis- 
placed elements are scalariform tracheids similar to those above 
mentioned. Radial sections through the region of the cambium some- 
times show that a portion of a xylem strand will be in its normal 
upright position for some distance, and then it will suddenly bend 
outward into the bark and become lost. Cambium cells usually 
accompany these, showing that such strands have been formed in the 
place that they occupy, and that they have not been formed in their 
normal position and then thrown out of place by the subsequent 
growth of the knot. 
In referring to the structure of the knot Duggar (2) states, prob- 
ably basing his statement on some previous article, ''Bast fibers, 
parenchyma cells, and even vessels may be found in this heterogeneous 
mass in which all of the associations of cells normally present have 
