THE ANATOMY AND OTHER FEATURES OF THE " BLACK KNOT" 121 
disappeared. This abnormal condition is apparently brought about 
by the breaking up of the cambium and a resulting development of all 
the various cell forms to which it may give rise in the diverse isolated 
areas." This is the prevailing idea concerning the development of 
the knot, but that it is not entirely correct is shown by the descrip- 
tions that have been given. The cambium as a whole retains its 
normal position between the xylem and phloem, and forms a more or 
less broken cambium ring through all stages. It is only from the 
broken up segments of the cambium opposite the broad rays, that 
these misplaced elements arise. 
The changes that take place in the bark, during the first season's 
growth after infection takes place, are not so marked as are the 
changes in the xylem. The rays broaden, continuous with the broad 
rays in the xylem, and they may become bent more or less. The 
bark may thicken to some extent but the thickening is seldom very 
pronounced. The phloem is evidently not greatly interfered with 
physiologically, because vigorous shoots may continue to develop from 
the knot and from beyond it, during both the first and second seasons' 
growth after infection becomes evident. This may happen even on 
stems that have become completely girdled. Where parenchymati- 
zation has been very pronounced in the xylem, and when isolated 
segments of summer wood are not produced during the first season's 
development of the knot, the cambium may disappear and there 
will be no line of separation between wood and bark. In such cases, 
however, the cambium is reorganized at the beginning of the following 
season because xylem wedges are always formed across such areas. 
The changes that take place in the bark during the second season's 
development of the knot are probably as great as those that take 
place in the xylem. Owing to the extension of the rays from the 
xylem into the bark, the breaking up and disorganization of the 
segments of the cambium opposite the rays, and the subsequent 
development of these cambium cells into their various elements, it is 
difficult to determine what part of the tissue in this portion of the 
knot arises from cells normally present, and what part from cells that 
have become pushed into it. A considerable amount of phloem is 
produced, usually in triangular shaped masses opposite the xylem 
wedges (see fig. 7) . The outer part of the bark is not materially altered. 
A short time before the conidia appear in the spring, longitudinal 
cracks are formed in the cork, over such areas, disclosing the greenish 
