218 REPORT OF THE BOTANICAL DEPARTMENT ‘OF THE 
of the trees, and had it not been for these combinations the result- 
ing damage would have been comparatively small. 
OBSERVATIONS. 
KINDS OF WINTER INJURY. 
Winter injury is usuaily classified under three heads, root in- 
jury, trunk injury and branch injury. In the last class may be 
included the destruction of fruit buds. 
Root injury, the freezing of the roots causing death or injury, 
occurs at times in the winter when the temperature is un- 
usually low and the ground is bare. In some of the Western 
states this is a common and serious trouble, but it is unusual in 
New York except on very light soils and in exposed locations 
where the snow blows away and no mulch or cover crop is used 
to cover the ground and hold the snow.’ 
Trunk injury may be due to the freezing, causing death 
or injuries within the trunk or limbs, of the active tissue known 
as the cambium, a thin layer of succulent formative cells between 
the wood and the bark, from which new tissues are developed. 
When the temperature is so low as to destroy the cambium layer 
the tree dies. However this layer is capable of withstanding 
much cold and of recovering after a severe injury. It was injury 
of this kind that was common and serious in New York State in 
1904. 
Branch injury is the killing back of the new and tender wood 
from the tip to a definite place. This form of injury occurs to 
some extent every year and depends very largely upon whether 
the wood ripens well or grows late in the fall and contains a 
large amount of moisture. 
HOW COLD CAUSES INJURY. 
The earlier plant physiologists believed that the death of 
plants was caused by the water in the cells freezing and the 
resulting expansion bursting the cell walls, thus permanently 
disorganizing the tissues of the plant which resulted in its death. 
Later investigations showed that this theory was incorrect, 
and that instead of the water freezing within the cells the cold 
*Green, W. J.,and Ballou, F. H. Winter Killing of Peach Trees. Ohio 
Agr. Exp. Sta. Bul. 157, p. 119. 
