120 Principles of Plant Culture. 
ering such plants with straw or other litter, or witb the soil, 
we lessen to some extent the intensity of the cold, but — 
more important,— we prevent frequent freezing and thawing 
(190d), and in a great measure, the heaving of the ground, 
which on heavy or wet soil is very destructive to the roots 
of many plants. A covering of straw, leaves or other litter, 
is preferable for low, herbaceous plants, as strawberries. 
The covering should not exceed an inch or two in thickness, 
otherwise the plants may be smothered in warm winter 
weather. For taller plants, as the grape and raspberry, the 
soil is usually the most convenient and satisfactory cover- 
ing, as a litter covering tends to attract field mice, that 
often injure woody stems, To assist in bending down the 
stems, a little earth is usually removed at the base on the 
side toward which they are to be bent. Shrubs too large 
for bending down may be inclosed in straw or similar 
material. 
203. A Northerly Exposure is generally Least Try- 
ing to Plants in wiuter, because it is least subject to fluctua- 
tions in temperature. The influence of the sun is here less 
perceptible, and snow remains longer than upon other ex- 
posures. Conversely, a southern exposure is most trying 
for the same reasons. The summit of a hill is usually less 
trying than a valley, because the cold air tends to seek the 
lower levels, especially in still weather (210). . 
204, Wind-Breaks, i. e., plantings of trees intended to 
break the force of prevailing winds, act beneficially in les- 
sening damage from cold, in so far as they prevent snow 
from drifting off the soil, and mitigate the effects of drying 
winds (190c). 
