92 The Principles of Fruit-growing. 
are useful. A mixed plantation, with the hardiest 
and most vigorous deciduous trees on the windward, 
is probably the ideal artificial shelter belt.* 
PROTECTING PLANTATIONS FROM FROST. 
Having now considered the relations of location, 
site and wind-breaks to cold and frost, we may ad- 
dress ourselves to a discussion of the means by which 
injury from local frosts may be averted, in case they 
threaten to occur. These means are of two types,— 
those which attempt to enable the plant to escape 
injury from the frosts, and those which attempt to 
prevent the frost from occurring. Altogether there 
are six general means which have been proposed for 
protecting plants from frost: Mulching, covering the 
plants, adding the vapor of water to the atmosphere, 
making artificial clouds, causing currents of air, and 
heating the air. T 
Mulching to enable plants to escape frost.t—It is 
a general opinion that a mulch or heavy cover placed 
upon the soil about plants when it is frozen will re- 
tard flowering and the maturing of fruit; yet the 
practice appears to be often unsatisfactory, and there 
are reasons for supposing that the philosophy of the 
subject is not commonly understood. The subject is 
one of increasing importance, for it is essential that 
* Bull. 48, Neb. Exp. Sta., on wind-breaks, comes to hand as we go to press. 
tA seventh category may be added,—whitewashing the plants. See Whitten, 
Bull. 38, Mo, Exp. Sta., and Garden-Making, p. 64. 
{Consult Bull. 59, Cornell Exp. Sta. 
