— 16 — 
last weighed, on the eighth of January 1898 showed a loss 
of water by air drying of 39.36 per cent, and branches from 
the same trees lost in the same time 42.24 per cent. The 
weights are not yet quite constant, but the figures may be 
taken as an approximate showing of the moisture contained 
in normal tissues in midwinter. But this moisture is not in 
the easily freezable liquid form; it is distributed as a con- 
stituent of cell wall, and in the viscid or solid cell contents, 
and can only be withdrawn and crystalized under the pro- 
longed action of extreme cold. Suppose a tree thus nor- 
mally constituted to be subjected, during the winter or early 
spring, to a period of warm bright weather. The influence 
of the sun’s rays penetrates the tissues, the cell contents be- 
come less viscid, water taken in by the roots still further 
liquifies these cell contents, there is movement within the 
cells and they become turgid with fluid sap. A sudden 
change marked by temperatures below zero occurs. There 
is a gradual shrinking of the tissues until the point of 
actual freezing, or crystalization is reached, and then comes 
that familiar and seemingly resistless expansion. If the 
sap-gorged tissues escaped rupture during the process of 
shrinking they are sure to yield to the expansive force ac- 
companying congelation. 
This form of injury is usually worse on plums, cherries, 
and peaches, than upon apples and pears. The cracks are 
less likely to heal; they more often increase in size, and the 
exudation of gum is followed by rot which leads to the 
death of the tree. 
With all trees this trouble can be in large measure pre- 
vented by providing some protection against the sun. This 
protection is most needed when the trees are young; as they 
attain size they in a measure protect each other. Various 
devices have been used, but we find wrapping with burlap 
the cheapest and most effective. Burlap that has been 
used for baling was purchased at dry goods stores at two 
cents per pound. One pound supplies twelve strips four 
inches wide and three feet long, and one strip is sufficient 
for a reasonably low-headed tree three to five years in 
orchard. The burlap being cut, and strings of proper length 
at hand, one man will wrap the trees at the rate of 60 an 
hour. The cost is thus nominal and the protection afforded 
ample. 
More serious than the the frost crack is that mechanical 
injury which is characterized by a separation of the bark 
from the wood. It has thus far been reported upon apple 
