100 
from frosts is experienced. There are 
many places in our mountains known as 
thermal belts, which are said to be en- 
tirely free from frost. Whether or not 
this is claiming too much, it is certain 
that distinct lines can often be seen sep- 
arating bright, fresh verdure above and 
blackened, frost-bitten foliage below. 
Similar lines of demarcation can be seen 
in spring between the early growth on 
the hillsides and the dormant buds of the 
valley below. In summer over the same 
area can be seen a distinct cloud line 
marking the height of the fog in the 
valley below, while above it on the hill- 
side will be cloudless air bathed in sun- 
light. In the fall, when frosts have 
claimed all the tender vegetation of the 
valley, there will be seen longitudinal 
bands skirting the hillsides, showing for 
a month or six weeks all the freshness 
of summer. Though the exact borders of 
these thermal zones cannot be located 
with precision, their general position is 
fairly constant. Orchards planted on 
thermal belts are remarkably regular in 
fruit bearing. There are many orchards 
in the mountains where old settlers claim 
they have never seen a failure in a crop 
from frost. The reason for these peculiar 
phenomena is undoubtedly the draining 
of cold air from the hillsides and its 
stratification in the valleys below. There 
are other circumstances connected with 
thermal belts that have not yet been fully 
worked out. However, there is at pres- 
ent sufficient practical evidence of the 
value of thermal belts in frost protection. 
Fruit growers should not fail, where pos- 
sible, to take advantage of them in or- 
chard planting. 
W. N. Hurt, 
Raleigh, N. C. 
Rolling Land North Slope 
The pest site for an orchard is gently 
rolling land with a north or northeast 
Slope. Always avoid flat land or valleys 
for cold air, being heavier than warm 
air, settles to the lower places and frost 
is more likely to kill the blossoms in 
such locations. If planted on the south 
side of a hill the trees will be warmed 
by the sun in spring, and, being pro- 
tected from the cold north winds, will 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
blossom early and may be killed by frosts, 
On the north slope the cold winds wil] 
keep them in a dormant condition longer 
or until danger of frost is past. Much of 
the land that is too hilly for profitable 
production of other crops will produce 
good crops of apples if given the proper 
care and attention. 
H. C. Tirumpson, 
Agricultural College, Mass 
Air Drainage and Frost 
In mountain regions, besides the 
draining of water from higher to lower 
levels, there is a Similar drainage of air 
This latter might seem to be of trifling 
importance in fruit growing, but it is in 
fact one of the most important considera- 
tions, for it tends greatly to avert frost. 
Freezes and frosts are undoubtedly the 
greatest hazard of the business of fruit 
growing. No disease or depredator de- 
stroys half so many hopes and dollars 
for the fruit grower as a few hours of 
frost. We are told that “the frust falleth 
alike on the just and on the unjust,” but 
in seasons when the daily papers are her- 
alding reports that an untimely frost has 
taken the entire fruit crop of the state 
some lucky fellow high up in his moun- 
tain coves, with not too many good works 
to his credit, has his entire crop saved as 
if by miracle. Frosts appear to strike in 
a very erratic manner; they are, however, 
like other phenomena of nature, subject to 
very definite laws. It is well known that 
as air becomes heated it ascends, and as 
it cools it becomes heavier and falls. On 
sloping ground air as it cools passes 
down from higher to lower levels. Other 
things being equal, low lands are more 
frosty than higher lands, because the 
cold and frosty air drains from the higher 
and settles into the lower levels. A corn 
field in the fall gives one of the best il- 
lustrations of the places most subject to 
frost and those also which are exempt. 
On the bottom lands the blades and stalks 
Will almost invariably show where frost 
has bitten first. Up on the hillsides and 
higher elevations the corn will often be 
found growing fresh and green, while in 
the bottoms below not a green stalk can 
be seen. Where knolls occur in bottoms 
