IO 
A. V. Duthie. 
lighter and darker striations is extremely regular as may be seen to 
the right of the diagram (Text-fig. 4.) Fig. 4 is a photomicrograph of 
part of a transverse section cut through this abnormal region. It 
shows regularly-arranged groups of strongly-thickened fibres which 
resemble closely those formed in the normal bast and are in contact 
with vertical rows of crystal-containing parenchymatous cells. 
Alternating with these bands of fibre-groups are zones consisting of 
thick-walled pitted parenchymatous cells often arranged concen¬ 
trically and intermingled with crushed tanniniferous cells. A few 
sclerotic nests similar to those found in the normal cortex are 
also present. A careful examination of transverse and longitudinal 
sections cut through this region has led to the conclusion that the 
Text-fig. 3. Transverse section of part of oak stem showing callus 
tissue formed from living cells of medullary rays. 
abnormal tissue has originated in a callus produced by the out¬ 
growth of the living medullary-ray-cells at the surface of the wound : 
this has in its turn been overgrown by an investing layer produced 
in the usual way. Apparently the newly-formed layer of normal 
wood was wounded in much the same manner the following year, 
and again healed by the development of callus-tissue from the living 
cells of the medullary rays. 
A second slab of oak from the same stem was examined and 
showed another case of wound healing very similar to the above, 
but differing from it in that the callus-cushion overarching the 
abnormal tissue was more distinct. 
In this connection it is interesting to notice that Hartig 1 
described and figured a case of wound healing in the oak by the 
formation and fusion of club-shaped swellings from the exposed ends 
of the medullary rays. The process was, however, not complicated 
1 Hartig. Forstliche Culturpflanzen. 
