176 
“Frost-Cracks”” 
“Frost-cracks”’ are formed in winter and are due to extreme 
changes in ee ois the tissues a occur on those 
portions of the tree where the maximum amount of heat is 
evi eloped, pee a on the ue side et the tree. Se the 
d gener- 
ally between 2 and 3 P.M., that portion of a tree trunk coinciding 
with the direct rays of the sun at this period is the one mos 
b : 
the location of frost-cracks e coincides with that area 
ving the minimum electrical resistance, and s the electrical 
resistance of a tree is proportional to the temperatures of 
ul n 
responding with the higher temperatures—that portion m of the 
tree showing the least electrical tible to 
frost-crac 
The opening and closing of frost- cracks are very responsive to 
ry un toa n 
than during low barometric pressure. Various fruit and shade 
trees are susceptible to frost cracks and the principal injury 
caused is to induce a tending to bleeding. 
“Sun-ScaLD” 
oe is comes “sun- eel is associated with severe and 
Ci 
tate occur either in the winter or in summer, When coniferous 
trees are likely to suffer ae sun-sca d. he moose-maple, 
shade trees the weenanes is one of the most subject 
to sun-scald; also among fruit trees and shrubs various kin 
are affecte un-scald is more likely occur on ned 
re : 
apple trees than on pruned ones, or on shaded limbe oe 
