452 MINNESOTA STATE HORTICULTURAL SOCIETY. 
plants or fruits. Moisture in the air, whether invisible or not, tends also 
to prevent the loss of heat from the ground by radiation; on the contrary, 
a limited amount of moisture in the soil tends to increase the danger from 
frost by increasing the evaporation and the consequent loss of heat at the 
surface of the earth and plants. 
It is evident, then, that fruit and vegetable growers in the hilly or roll- 
ing sections, like most of Ohio, should so place their earlier and more tender 
crops as to avoid the lowlands and valleys and very wet lands, and plant 
on the hillsides or ridges; or, whenever it is possible, to take advantage 
of bodies of water and plant on the leeward side. An intelligent and experi- 
mental study of these conditions and locations must be made, however, by 
each one for himself. 
The artificial appliances for protecting crops against frost are based upon 
the following effects and conditions or a combination of them, for one re- 
sult is never obtained without the others also, to a partial extent at least: 
to actually cover or roof in the plants; to prevent a rapid radiation of heat 
from the earth; to increase the moisture in the air; to directly warm the 
air; to create artificial drafts, whereby the air is mixed and the cold air is 
not allowed to lie at the surface of the earth. 
Covering with screens of any sort must necessarily be limited to small 
lots because of the expense, but strawberries and other low plants may be 
effectively protected with straw or hay, and frequently young potatoes may 
be saved by covering them with earth by means of the cultivator or plow. 
Radiation of heat may be checked by building frequent smudge fires on the 
windward side of the orchard or field, particularly on limited bottom lands, 
where the smudge would not move far. But when, to secure the smudge, 
a material is used that will also add moisture to the air, the cheapest and 
most effective plan is probably in operation. The smudge of vapor and 
smoke may be secured by building frequent fires of damp straw or stable 
manure about the orchard or field. A good method is to pack damp stable 
manure into common grain or burlap sacks. They should be distributed 
through an orchard in rows about one hundred feet apart and about fifty 
feet between sacks in each row. When it is necessary to use them, a small 
amount of coal oil should be poured on each sack and ignited. It is usually 
unnecessary to fire more than every second or fourth sack. These sacks will 
burn with a smouldering fire for several hours, The amount of heat set free 
by burning one sack of manure weighing fifty pounds and condensing the 
water vapor near the earth would be sufficient to raise the temperature 
twenty degrees in a space seventy-five feet square and twenty-five feet deep. 
If one-fourth of this heat remained within this area it would give ample pro- 
tection during an ordinary frost.. Bales of wet straw have been successfully 
used. One hundred pound bales were cut into four pieces and properly 
dampened. 
The best plan of all, however, is to use portable smudge fires. A wire 
netting can be stretched from four stakes on a low truck wagon or sled and 
covered with a considerable thickness of wet manure. Dirt is then thrown 
on the wagon body to protect it, and pots of burning tar or oil are set under 
the straw. A barrel of water is carried on the wagon to keep the straw wet. 
* In this way the fire can be moved wherever it is most needed, which is gen- 
erally along the windward side of the orchard, but which may be in the low- 
est place; the loss of heat by an upward draft is prevented, and instead it has 
