FROST 
this can be done in a measure, but there 
is much to be learned and much to be 
accomplished before we can be fully as- 
sured against losses caused by cold. 
Frost occurs only during calm, cold 
nights when the mercury is as low as 32 
degrees Fahrenheit. This statement 
makes it necessary to distinguish between 
a frost and a freeze. There can be no 
frost without freezing, but there can be 
a freezing temperature without frost pro- 
vided there is little moisture in the air. 
Freezing occurs at that degree of tempera- 
ture at which water will solidify; or at 
which ice will melt. Thus the freezing 
point and the melting point, or the point 
of fusion, are one. The freezing point of 
water is 32 degrees above zero; the freez- 
ing point of mercury is 39 degrees below 
zero; the freezing point of sulphuric ether 
46 degrees below zero, and the freezing 
point of alcohol, 203 degrees below zero. 
The freezing point of water is the approx- 
imate danger point of vegetable life. We 
call the degrees of the thermometer be- 
low the freezing point, degrees of cold; 
the degrees above the freezing point, de- 
grees of heat. When the atmosphere 
which comes in contact with the body of 
a plant or animal is colder than the body, 
it absorbs heat from the body and is 
called cold, because it is so in relation to 
the temperature of the body. All animals 
and plants have a certain power of main- 
taining the heat of the body in defiance of 
external cold. This power in animals is 
due to the process of combustion, in which 
carbon and hydrogen taken into the sys- 
tem as food, unite with oxygen. This is 
accomplished by means of breathing, 
which oxygenizes the blood. The normal 
heat of the blood of birds is 100 to 112, 
while in mammals it is 96 to 102. Thirty 
degrees below this normal temperature is 
almost sure death, because at this point 
circulation stops; while ten degrees above 
is almost equally dangerous, for then the 
system is consumed by heat. Plants, dur- 
ing the summer, store food; they breathe 
and manufacture heat out of food parti- 
cles just as do animals, but not in the 
same degree nor in the same manner. 
Plant life resists cold by the radiation of 
heat. There is considerable difference in 
‘grees above zero; 
1007 
the rapidity with which the different va- 
rieties of plants give off heat. This can 
be illustrated by the differences of radia- 
tion in soil, rock and water. Animals 
know that during the cool nights of 
spring and autumn, after the earth has 
become cool, by huddling up against a 
large rock they can keep warm. It has 
held its heat longer than the soil. 
Horticulturists know also that adjacent 
to large bodies of water the temperature 
is modified by the radiation of heat from 
the water after the soil has lost a much 
greater degree of heat. An illustration 
of this is seen in Western Michigan along 
the eastern shore of the lake, where a 
strip of territory about 15 miles wide and 
150 to 200 miles long is protected against 
cold by the milder temperature of the lake 
during the cold season, and that region 
is a good fruit-growing section, whereas 
other portions of the state grow compara- 
tively little fruit. 
Danger Point 
There is considerable difference in the 
power of plants to radiate heat, and in 
the rapidity of radiation, and these facts 
determine in a large measure their re- 
sisting power to a temperature greater 
than that of their bodies. It is very in- 
teresting and yet very difficult to 
determine with exactness the _ de- 
gree of resisting power belonging to 
any particular plant, for there are so 
many counter influences that modify any 
rules. The Missouri Agricultural Experi- 
ment Station has found that dormant 
peach buds can stand a temperature of 
eight or nine degrees below zero with no 
injury. When the buds are appreciably 
swollen, zero weather is the danger 
point; when the buds are showing pink, 
they can stand 15 degrees above zero; 
when the buds are almost open, 25 degrees 
is the danger point; when they are newly 
opened, about 26 degrees would be the 
point of danger; when the petals are be- 
ginning to fall, 28 degrees above zero is 
cold enough to cause uneasiness; when 
the petals are off, they can stand 30 de- 
when the “shucks” 
(calyx tubes) are beginning to fall off, 
32 degrees above zero is the danger point. 
This shows the different degrees of resist- 
