THE ANATOMY AND OTHER FEATURES OF THE " BLACK KNOT" I23 
breadth has become greater than the combined breadth of the three 
preceding rings of growth just inside of it. The cortex opposite this 
portion is not ahered. It is interesting to note that while strands of 
hyphae can easily be seen on the opposite side of the knot, even under 
a very low magnification, apparently none are present in either the 
wood or bark on this side. A broken cambium ring, made up of dark 
colored segments opposite the xylem wedges, can be seen to be con- 
tinuous with the cambium opposite the xylem on the lower side of the 
figure. Farlow (3, p. 445) says : If in midsummer or winter we make a 
cross section of a knot more than a year old we shall find one more 
layer of wood on the sound side of the stem than on the side of the 
knot. In other words, on one side, the formative power of the cam- 
bium has expended itself in forming a new layer of wood and bark 
(phloem), and, on the other, irritated by the presence of the fungus, 
it produces a mass, the knot, in which all distinction between wood 
and bark has been lost." A large number of knots have been ex- 
amined during the second season of their development, but so far 
none have appeared which do not reveal a condition similar to that 
shown in fig. 9. This section shows the same number of rings of 
growth on both sides of the stem, the outer ring being represented 
by the xylem wedges on the infected side. A condition similar to 
this will always be found unless infection took place near the beginning 
of cambial activity the year before. In such cases the second ring of 
growth inside the cambium may not be seen because it is usually trans- 
formed into parenchyma, or if xylem was formed it has been pushed 
out of place by the growth of the knot as has been described. Cross 
sections of knots a year older than the one shown in fig. 9, will still 
show the xylem wedges if the interior of the knot has not been too 
badly destroyed by insects. 
Small triangular-shaped masses of phloem are present opposite the 
most of the xylem wedges but the magnification in fig. 9 is too low 
to show them. They can be seen however in fig. 7. The dark zone 
around the outside of the section is the stroma containing the peri- 
thecia. 
In stems younger than the one shown in fig. 9, a large cavity is 
sometimes formed in the center as the knot develops. In such cases 
it seems evident that a pulling force has been exerted and that the 
thin ring of xylem around the pith has not been strong enough to 
resist it, so it becomes pulled apart and may become more or less 
