490 
J. G. GROSSENBACHER 
loose bark outward, while if no radial cleft occurs the enlargement 
may look like that on a maple trunk shown in Fig. 40, Plate XXV. 
The resulting repair growths are not always uniform even when they 
follow the kind of initial injury that separates the bark from the wood. 
In some cases the loosened bark has but few injuries (Fig. 3, Plate 
XXI) ; in other cases, or perhaps even in other portions of the same 
affected area, the outer phloem as well as the cortex may have so 
many groups of dead cells scattered among the living parts that 
the entire bark dies. That has been the case in the lower portion of 
the stem part shown in Fig. 40. A section through the upper part 
of this maple trunk reveals a condition like that shown in Fig. 37. 
Here the discolored line oc represents the position of the cambium 
when the injury occurred. The initial injury not only resulted in a 
line of separation in the inner phloem like that shown in Fig. 3, but 
involved cell-groups in the cambium proper as well as in the middle 
and outer bark. As in the case shown in Fig. 3, however, the inner 
phloem had sufficient living connection with the wood to permit the 
development of a cambium that persisted, excepting in the bare 
region shown toward the lower end of Fig. 40, where it died along 
with the loosened bark outside. A cambium also developed in the 
inner part of the loosened bark shown in Fig. 3, running through 
the outer phloem. After the production of a sheath of new cells in 
this new growing zone, the middle ones became wood and those along 
both outer sides continued as cambial zones. In that way one growing 
zone was converted into two, which separated more and more as the 
older cells toward the middle were converted into wood. The sheath 
of new wood {nw) just within the old outer bark {oh, Fig. 37) arose in 
that manner, and has a cambium on each side. The low-power 
views shown in Fig. 36 {a-e) are photographs of sections cut from 
blocks obtained from the specimen shown in Fig. 37. Fig. 36a shows 
the old outer bark {oh) of Fig. 37, with only a small portion of the 
new cambium {nc) included. The new bark shows compressed inclu- 
sions of dead tissues resulting from the initial injury. Figs. 36^ and 
36^/ are so tightly pressed against each other in Fig. 37 that the two 
barks seem to be one. Fig. 36^ is taken from the line oc in Fig. 37 
and shows more clearly the similarity of this line to the figures ob- 
tained from apple, such, for example, as Fig. 18. Fig. 39 is a more 
highly magnified view of a portion of Fig. 36^. It shows the presence 
of dead groups of old cambium cells adhering to the old wood {ow). 
