5o8 
J. G. GROSSENBACHER 
of immaturity or arrested development. It seems possible that, at 
least in some cases, the presence in the bark of metabolized foods of 
insufficient concentration to allow normal growth and maturation 
is the most significant phase of immaturity; the occurrence of droughts 
appears to have a significant relation. An adverse period in the 
environment occurring at such a time stops the further accumulation 
of the labile components of protoplasm, and a long retention of these 
elementary constituents, together with the enzymes present, may 
lead to catabolic processes that eventually result in the death of the 
tissues involved. 
Acknowledgments 
In this connection it is a pleasure to acknowledge the aid received 
from Professors J. B. Overton, L. R. Jones, and E. M. Gilbert, of the 
University of Wisconsin, during the winter of 1911-12, and especially 
that of Professor C. E. Allen, of the same institution, for the many 
excellent suggestions he made regarding the revision of this paper. 
DESCRIPTION OF PLATES XXI-XXVII 
Plate XXI 
Sections of material collected before growth started in the spring, showing types 
of initial injuries. All from apple excepting Figs, i and 2, which are from pear. 
Fig. I. Injury mainly in cambium, phellogen, and phloem regions; scattered 
cell-groups in xylem and cortex affected, as indicated by discolored places. 
Fig. 2. Another section with severe initial injuries confined chiefly to inner 
cortex and outer phloem; phloem rays and cambial zone also injured. Scattered 
groups of dead cells in other parts of cortex and phloem. 
Fig. 3. Section of apple branch with common type of injury not usually 
accompanied by much discoloration, consisting principally of a rupture in the 
inner phloem and only secondarily of groups of dead, discolored cells. 
Fig. 4. Section of apple with most of the injury in the inner phloem, as indi- 
cated by discolored streaks and masses. On the left the cambium is killed; on the 
right it is alive and apparently normal. 
Fig. 5. A condition comparable with that of Fig. 4, excepting that a portion 
of the injury consists of ruptures as shown near the right. 
Fig, 6. Some living cambium on the right, and a zone of severe injury in the 
inner phloem above; on the left most of the cambium is killed. The rays are more 
severely affected than in the section shown in Fig. 5. 
Fig. 7. Collapsed tissue in the inner phloem and cambium is interspersed 
with a few living cells. Phloem rays are dead, and scattered groups of dead cells 
occur in the older portions of the phloem. 
Fig, 8. Some groups of dead cells and some ruptures occur in the cambium; 
the inner phloem has but few affected cells. The middle and outer phloem are 
considerably injured. 
