CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 49 1 
It is evident that in most places along the line oc of Fig. 37 the cam- 
bium, giving rise to the new wood inw) outside it, also arose much 
like that shown in Figs. 14, 15, and 17, from cell divisions occurring 
in the adhering layer of phloem (Fig. 3). Trecul^ seems to have 
obtained very similar results by palling loose and then tying back a 
piece of bark. 
Fig- 39 shows another fact of special interest, for it makes it 
apparent that much of the new wood formed about the original line 
of injury subsequently dies and becomes discolored. Even in portions 
of the line cc of Fig. 37, where the new wood is practically continuous 
with the old and where the rays are not even interrupted, there has 
been more or less of this discoloration and dying of the new wood, 
as shown in Fig. 42, Here the initial injury seems to have involved 
chiefly the outer end of the wood rays and scattered, but small, 
groups of cambium cells. Nevertheless a narrow, ragged-edged zone 
of new wood died and became discolored, as Fig. 42 shows. 
The Development of Crown-Rot from the Initial Injuries. — As sug- 
gested above, bark-injuries may or may not be accompanied by evident 
radial clefts, and when they are not evident externally they are yet 
often present, as may be gathered from .Fig. 36a. The old bark (ob) 
is shown to be run through by numerous small, radial rifts that repre- 
sent incomplete ruptures which were afterwards filled by prolifera- 
tions from adjoining cells. Fig. 38 shows a case of this kind, also 
in maple, where apparently the bark was only separated from the 
wood, and yet where so many of these tiny radial rifts occurred that 
the bark involved is evidently dying. In this case the whole of 
the cambium as well as much of the inner phloem died as a result 
of the initial injury. The rest of the bark was still alive when cut 
on May 28. Although no definite new cambium had yet developed 
in this loosened portion of bark, the spring growth of wood is seen 
to be considerable on both sides of the wound. Callus-roll formation 
has made an evident beginning around the injury, even though the 
bark involved is not dead. 
On the other hand. Figs. 43 and 45, Plate XXVI, show apple 
trees in which internal bark-injuries, resulting in a separation of the 
bark from the wood, were accompanied by evident radial clefts. 
The former is shown before and the latter after the loose bark was 
^ Trecul, A., Production du bois par I'ecorrc des arbres dicotyledones^ Ann. 
Sci. Nat. Bot. Ill 19: 257. 1855. 
