504 
J. G. GROSSENBACHER 
more years after the forest has been thinned. Hartig^^ gives some 
interesting data along this Hne and concludes that the injury results 
from the contraction and expansion of the bark rather than from the 
heating of the sun as is maintained by many, because he found frequent 
cases of it on north slopes and on the east and north sides of trunks. 
Many of the sections used in the present histological study of 
crown-rot were made from the bases of shoots arising from large 
branches of apple trees that had been pruned rather severely, and 
they therefore also represent the initial injuries preceding the develop- 
ment of crotch cankers as more fully discussed on pages 40-42 of 
my paper written in 1912. Goethe published a paper in 1877, in which 
he announced the conclusion that cankers are due to low-temperature 
injury of the bark. When it was pointed out to him that in Italy 
where the winters are mild cankers are equally prevalent, he reinvesti- 
gated^^ the matter and revised his conclusions to the effect that many 
of the cankers are due to fungus parasites. It should be noted, 
however, that his revised conclusion was based largely on the fact 
that in the spring of 1878 he found new cankers even though no late 
frosts had occurred. (The notion that only late frosts cause these 
injuries has led many astray.) Fungi developed on cankers when 
placed in moist chambers, but when spores were used on uninjured 
bark no cankers resulted. In the following winter bark injuries were 
numerous in crotches and other places where cankers usually occur. 
Many of the wounds were carefully cut out in April and most of them 
healed rapidly, although in a few instances the branches involved died. 
Some years later, also, Goethe^* made an extended study of winter- 
injuries, giving particular attention to the aftermath or the results of 
such injuries. A drop in mid October to — 2.5° C. and one to — 10° C. 
in November very severely injured the pith and other tissues in 
shoots and the bark of trunks just above the ground. High-headed 
trees were found more subject to trunk injury than low-headed ones. 
This is in agreement with what I found in western New York (Tech. 
Bull. 23, pp. 18-20). Goethe described interesting cases in which 
^2 Hartig, R., Ueber den Sonnebrand oder die Sonnenrisse der Waldbaume, 
Untersuch. Forstbot. Inst. Miinchen i: 141. 1880. 
Goethe, R., Mittheilungen uber den Krebs der Apfelbaume. Leipzig. 1877. 
, Weitere Mittheilungen iiber den Krebs der Apfelbaume, Landw. Jahrb. 
9: 837. 1880. 
Goethe, R,, Die Frostschaden der Obstbaume und ihre Verhutung, Nach den 
Erfahrungen des Winters 1879-80, dargestellt. Berlin. 1883. 
