CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 5OI 
changes he records were mainly due to the subsequent increase in the 
activity of the oxidizing enzyme present in the injured tissues. From 
his experiments with low temperatures, Schaffnit^^ holds that tem- 
peratures a little above the freezing point induce chemical changes 
in the protoplasm that convert labile into more stable compounds. 
The discoloration noted in the new cambium of Fig. 31 , Plate XXIV, 
and in the new wood shown in Figs. 39 and 42, Plate XXV, is probably 
due to the diffusion into the new tissues of some injurious by-products 
from cells affected by the cold. This aftermath of low temperature 
effects seems to account for the fact that bark-injured trees may be 
sick for some time before they die or recover, and that some may 
remain dwarfed for years.^^ Miinch^^ found that the discoloration so 
commonly present in the heart wood of some trees is not due to sub- 
stances secreted by living cells, bat to oxidation products arising in 
dead cells. The presence of fungi increases the extent of the browning. 
Goethe^^ has also made notes on this diffusion into living tissues of an 
injurious substance from tissues injured by low temperatures. He 
found that even in cases of severe bark-injury on the lower portions 
of tree-trunks, the affected trees survived if this discolorizing substance 
did not diffuse throughout the sapwood, while if its diffusion was 
rapid and extensive the tree usually died in a fairly short time. The 
same facts were found to hold regarding branches at the crotches of 
which bark-injury had occurred. Soraijer^^ thinks it likely that the 
injurious substance which diffuses from dead protoplasm into sur- 
rounding cells is an enzyme which arose from the disintegrating proto- 
plasm. Active growth is said to check this diffusion or to make it 
harmless. Bailey^^ found, also, that oxidizing enzymes are largely 
responsible for discolorations developing in new green lumber during 
warm, moist weather. 
3° Schaffnit, E., Studien iiber den Einfluss niederer Temperaturen auf die 
pflanzliche Zelle, Mitth. Kaiser. Wilh. Inst. Landw. Bromberg 3: 93. 1910. 
Gutzeit, E., Dauernde Wachstumshemmung bei Kulturpflanzen nach voriiber- 
gehender Kalteeinwirkung, Arbeit. Biol. Anstalt Lands. Forstwirts. 5: 449. 1907. 
'2 Miinch, E., Uber krankhafte Kernbildiing, Naturw. Zeit. Forst-Landw. 8: 
533; 553. 1910. 
23 Goethe, R., Die Frostschaden der Obstbaume und ihre Verhiitung. Berlin. 
1883. 
24 Sorauer, P., Was bringen wir mit den Samenriiben und Samenknaueln der 
Zuckerriiben in den Boden? Zeit. Pflanzenkr. 24: 449. 1915. 
25 Bailey, I. W., Oxidizing Enzymes and Their Relation to Sap Stain in Lumber, 
Bot. Gaz. 50: 142. 1910. 
