Wound healing in a species of Oak. 
9 
Owing to the reduction of bark-pressure in the region of these 
injuries, broad callus lips have been produced which have arched 
over the exposed surface and finally coalesced (Text-fig. 2). As the 
exposed cambium perished completely there is no cohesion between 
the callus-tissue and the old wood. In several wounds a thin layer 
of entrapped cork was found between the callus cushions, and the 
remains of cortex and bast, which developed on their rounded 
surfaces before these met and fused, can be seen distinctly. Par¬ 
ticularly noticeable are the groups of sclerotic cells which appear as 
Text-fig. 2. Transverse section of part of oak-stem showing wound which 
has healed completely in two years. 
more or less translucent brown specks embedded in masses of thick- 
walled cells with tanniniferous contents. As healing proceeded the 
callus lips pressed closely against each other, displacing the outer 
tissues, until finally the cambium layers came into contact and 
thickening proceeded normally. Even after the wounds have 
healed completely the effect of the injury still appears in the 
broadening of the wood ring immediately following. 
All the wounds considered thus far have exhibited the usual 
method of healing by the formation of callus cushions from the living 
tissues at the edges of the wounded area. The remaining injury, 
which lies about 5 cm. to the right of the peg, has apparently healed 
in a somewhat different manner (Text-fig. 3). 
The broadening of the 114th ring is due to the lateral influence 
of a rind gall a little to the left, which is not shown in the diagram. 
The summer wood of each of the two succeeding rings passes into 
a tissue which at first sight suggests a portion of enclosed phloem. 
This abnormal tissue appears to the naked eye as a series of undu¬ 
lations each bordered by a darker line. In places the alternation of 
