502 
J. G. GROSSENBACHER 
It seems possible, too, that certain degrees of severity in the en- 
vironment disturb the equilibrium between the enzymes in cells that 
are in a susceptible condition, and thus eventually lead to disintegra- 
tion which ma}^ culminate in the death of the tissues. Such an assump- 
tion might lead to the surmise that the disintegrations evident in the 
cambial region shown in Fig. 31 are due to an excess of a hydrolyzing 
enzyme or to the absence of factors that normally inhibit hydrolytic 
action at a certain stage of growth, and permit the usual maturing 
processes to go on to completion. Lepeschkin's^^ studies of the effects 
of high temperatures on protoplasm, as well as some of the results 
noted by Overton^^ when using heat to kill portions of Cyperus stems, 
are interesting in this connection because they suggest the possibility 
that opposite extremes of temperatures may, after all, have some 
parallel effects. 
Although the researches that have been cited on the chemical and 
physiological phases of low-temperature injury are apparently of 
fundamental importance, they give only a very meager understanding 
of what seems to be a small portion of the process. As already men- 
tioned, some of the simpler physical effects of a lowering of the tem- 
perature must also be brought into proper relation with the physio- 
logical changes induced. After these simpler matters have been dis- 
posed of and a fair understanding of the development of bark injury 
has been attained, the practical phases of the problem will still be 
unsolved. One who has given this subject much thought cannot 
avoid the striking fact that in nature these injuries ordinarily occur 
not so much on account of the degree of the low temperature reached, 
as because of the condition of the bark at the time of its occurrence. 
Some Other Bark Diseases Resulting from Internal Bark 
Injuries 
In the course of my study of crown-rot some other bark diseases 
were also traced to their origin in bark injuries very similar to those 
often giving rise to crown-rot. The so-called "cankers," 'sun-scorch," 
and the premature roughening of bark on smooth-barked apple and 
pear trees were the types most commonly encountered. The latter 
2^ Lepeschkin, W. W., Zur Kenntnis der Einwirkung supramaximaler Temper- 
aturen auf die Pfianze, Bericht, Deutsch. Bot. Ges. 30: 703. 1913. 
Overton, J. B., Studies on the Relation of the Living Cells to Transpiration 
and Sap-flow in Cyperus, Bot. Gaz., 51: 28; 102. 1911. 
