MECHANICAL INJURIES 
TO WHICH 
FRUIT TREES ARE SUBJECT. 
The disease we have attempted to discuss is only one 
of the many sources of injury to which our fruit plants are 
liable. Aside from the numerous insect pests which are 
demanding constant attention, we have a long list of para- 
sitic fungi, and certain other mechanical injuries whith re- 
sult from peculiarities of climate. Some of these deserve 
brief mention here. 
The mechanical injuries referred to are commonly 
spoken of as ‘"frost-crack” and “sun-scald,” and both are 
referred to a combined action of sun and frost. Most of 
the cases of so-called sun-scald that have come under my 
observation have proved to be cases of blight upon the trunk 
or large branches. They are characterized by dark, dis- 
colored areas of dead bark, commonly circular or elliptical, 
but sometimes irregular in form, and most frequently, 
though not always on the side exposed to the sun. The 
dead bark as it dries shrinks and adheres closely to the 
wood. 
Frost cracks occur upon the exposed side of the trunk, 
extending longitudinally. They are produced in winter and 
early spring under the influence of extreme low. tempera- 
tures, and may, when growth starts close and entirely heal. 
The liability of trees to injury of this character depends 
mainly upon the amount of water contained within the tis- 
sues. Trees that grow late, and enter the winter with wood 
not thoroughly ripened, and hence containing more water, 
are more susceptible to injury than those that are enabled 
to ripen and harden the wood. Even well ripened wood 
contains normally about 40 per cent, of water. Trunks of 
apple trees cut on the fifteenth day of January 1897 when 
