488 J. G. GROSSENBACHER 
dead tissues predominate in the phloem. It may be noticed that on 
the left the bark is thicker than it is on the right. This results from 
the presence of larger groups of living cells in this portion of the 
phloem; indeed, it appears that groups of wood cells (appearing in 
the photograph as rather dim whitish patches) have in some way 
arisen in this region. The process had advanced further in the 
specimen shown in Fig. 24. Here some of the bark had died to the 
wood, and, because of the presence of much dead tissue in the inner 
phloem and the old cambium, the callus is a rather sickly affair. 
It includes the repaired phloem considerably speckled with masses 
of dead tissue, and the badly injured cortex. In the lower right corner 
occurs a strip (white) where the phloem is being transformed into 
wood cells, yet no definite cambium is in evidence. Although not 
shown in this figure, the slide from which this photograph was made 
shows abundant hyaline fungus mycelium in the dead bark, even in 
the dead cambium and the old inner phloem between the callus and 
the old wood. Fig. 25 shows a similar case in which the most severely 
affected area was very narrow, thus permitting its use in this study 
without its falling apart. In this instance the callus is much better 
developed, having a definite cambium and a layer of new wood. 
The old inner phloem and the old cambium were also dead for some 
distance back of the nose of the callus. Some fungus mycelium was 
present in the dead bark. Fig. 26 is made from the margin of a larger 
area that had sunken in, like that shown in Fig. 41 of Plate XXV. 
The marginal callus was much like that of Fig. 25, and the presence 
of fungus is indicated by the pycnidia (of Sphaeropsis?) showing 
under the periderm toward the left. 
On Plate XXIV are brought together some higher-power views 
giving greater detail, though in some instances cell outlines are 
necessarily more hazy. Figs. 27 and 28 show clearly the remains of 
the dead cambium and inner phloem; they also prove that even as 
late as the end of May substitution growth is in progress along the 
inner side of the repaired bark and has established better connection 
with the old wood. This latter fact is indicated by the presence of 
excessively large round cells, that appear to be filling the gaps left 
by the shrunken dead tissues. Fig. 30 shows the development of a 
new cambium (nc) between the dead inner phloem and sheets of dead 
tissue in the outer phloem. In Fig. 31, groups of dead cells appear in 
the former position of the inner phloem, around and among which 
