THE ANATOMY AND OTHER FEATURES OF THE BLACK KNOT" II5 
color. Cross sections of both primary and secondary infections may 
show either a small or a large part of the circumference of the stem 
altered as a result. In either case, however, there is probably a 
progressive growth of the fungus around the stem as the season 
advances, resulting either in the girdling of the stem or the alteration 
of only a sector of it. 
Abnormalities in the tissues of the stem caused by infection are 
usually deeper at the leaf gaps than in the internodes between, prob- 
ably owing to the fact that more parenchyma is present in such 
areas than elsewhere. Lodeman (5) suggests that the fungus gains 
entrance to the stem at the axil of the leaf or about the bud situated in 
its axil. The great amount of disturbance might also be accounted 
for by this means if it were not for the fact that the leaf gaps in stems 
infected secondarily show quite as much disturbance as those infected 
primarily. 
In young normal twigs of the choke cherry the rays are mostly 
uniseriate in the first ring of growth, with a few multiseriate rays two 
or three cells wide. In traumatic areas the multiseriate rays may be 
considerably broader in this ring, those having as many as seven cells 
in cross section having been noticed. Cross sections of six-year-old 
stems, such as is shown in fig. I, show a proportional increase in the 
number of multiseriate rays and occasionally it can be seen that the 
formation of these may come about by the fusion of adjacent uniseri- 
ate rays. Tangential sections of the older wood, fig. 3, show that 
approximately the proportion of uniseriate to multiseriate rays is as 
two to one. Parenchyma is confined largely to the rays with an 
occasional cell in among the fibers and other elements of the wood, the 
small development of wood parenchyma being a character common to 
all of the Rosaceae, except the Tribe Chrysobalaneae, according to 
Solereder (7, p. 309). The vessels are small in size and are usually 
arranged in one or more zones in the early spring growth, beyond 
which they may become scattered so that it is often difficult to deter- 
mine where the spring growth ceases and the summer growth begins. 
The tracheids in the normal wood are distinctly of the pitted type. 
The stimulating effect of the fungus first makes itself manifest ia 
the vicinity of the cambium in knots resulting from both primary and 
secondary infections, but the position and identity of the cambium 
as a whole is not so greatly changed as has been supposed. A portion 
of a cross section of a stem taken at Madison on April 6, approxi- 
