5o6 
J. G. GROSSENBACHER 
some cases also kill living portions while vegetating in severely injured 
bark. 
On Plate XXI are shown some of the main types of injuries often 
found in bark after unseasonably severe periods. This material was 
collected before evident growth started in the spring and therefore 
gives some idea of the actual distribution of the injuries. An examina- 
tion of these figures makes it appear that injuries are of two types: 
in Figs. I, 2, 4 and 8 they are evidenced chiefly by a discoloration and 
collapse of the affected tissues, whereas in Fig. 3 the injury consists 
mainly of a tangential rupture with only a few of the groups of dis- 
colored cells; in Figs. 5, 6, 7 and 9 there occur combinations of the 
two types of injury. In the latter cases the tissues along the margins 
of the ruptures are discolored and collapsed much as they are in Figs. 
1 and 2. Unfortunately the sections of the material having a combina- 
tion of the types of injuries shown in Figs, i and 2, or of those in Figs. 
2 and 7, turned out to be such poor preparations that no use could 
be made of them. 
Plate XXII shows comparable cases as they appeared about two 
weeks later. This represents a stage of regeneration growth during 
which living parenchyma cells surrounding injured or dead regions are 
actively proliferating into spaces formerly filled by the shriveling 
masses, and into gaps occasioned by ruptures. Figs. 10 and 12 are 
especially interesting because dead tissues are compressed into more 
or less radially arranged plates. The proliferating cells are seen to 
penetrate many of the dead masses, and apparently make contact 
with living cells beyond. This rapid early regeneration-growth in 
injured bark is responsible for the fact that so few injured places 
result in patches of dead bark. 
Practically the final alignment of injured and living tissues, as 
well as the locations of the new meristematic layers, is shown on Plates 
XXIII and XXIV. From these figures it is evident that when 
enough of the cambium and inner phloem are killed to form a fairly 
thick dead layer only a few, or in some cases over considerable areas 
no living connections are re-established between the old wood and the 
bark. In some instances the most severely affected bark died early 
(Figs. 24, 25 and 26), while in others (Figs. 18, 21, 22, 28, 31 and 32) 
regeneration went on rapidly and the formation of a considerable 
amount of new wood and bark resulted (Figs. 18, 22 and 31). There 
are some in which the outer bark has remained alive but in which very 
