1288 



FROST 



FROST 



perature is falling. (6) The frost-alarm thermometer is 

 a device for sounding an alarm when a certain tempera- 

 ture is reached. This point is usually a degree or two 

 above the danger point, and serves the purpose of 

 giving notice of approaching danger. The thermometer 

 is placed at a point any distance away and where the 

 lowest temperatures usually occur. Wires are led from 

 the thermometer to the house. When the mercury 

 falls below a certain point, the electric circuit is broken 

 and a relay causes a bell to ring. If a thermograph is 

 at hand, the man on duty may easily note by the 

 character of the temperature curve whether or not it 

 may be necessary to prepare for lighting the fires. There 

 are several types of frost-alarm thermometers on the 

 market, but the simplest and most trustworthy of all 

 is the one in which the mercuric column breaks an 

 electric circuit which in turn operates a relay con- 

 nected with an electric bell. 



Besides the above necessary devices for orchard- 

 heating, there have been invented certain automatic 

 devices for lighting a large number of pots at the 

 same time, either 

 by hand or elec- 

 trical control. Such 

 devices are always 

 complicated, and, dis- 

 regarding their cost 

 which is an item of 

 considerable impor- 

 tance, they are im- 

 practical in large 

 operations. If the 

 means be electrical or 

 mechanical, an expen- 

 sive cartridge must 

 be used, the cost of 

 which is greater than 

 the cost of the labor 

 for lighting the pots 

 by hand. Besides, all 

 automatic devices re- 

 quire that a large 

 number of wires be 

 strung through the 

 orchard, which would 

 interfere with other 

 orchard practice. As 



1588. Using wood for orchard heating fifty fires to the acre. 



a rule, the period over which frost-injury may occur 

 may be a month or six weeks, and during this time 

 various orchard work must be in progress. 



Injurious temperatures. The temperatures at which 

 the principal orchard fruits are liable to be injured 

 cannot be accurately stated, since weather conditions 

 previous to a freeze determine to a very great extent 

 the ability of plants to withstand low temperatures. 

 Not only do the different degrees of cold produce dif- 

 ferent effects on the same plant, but the same plant 

 will often behave differently when subjected to the 

 same degree of cold. It is well known that plants or 

 parts of plants in active growth are more easily killed 

 by low temperatures than the same plants or parts of 

 plants when dormant. Actively growing plants con- 

 tain large quantities of water; that is to say, the pro- 

 toplasm or cell-sap is watery, and, as a rule, the larger 

 the proportion of water contained within the plants 

 the more likely they are to be injured by low tempera- 

 tures. Injury to plants is due to changes or disturb- 

 ances produced in the protoplasm by low temperatures 

 and, because of the unlike specific characters of dif- 

 ferent plants, is not always produced in exactly the 

 same way. Some plants are injured at temperatures 

 above freezing, while others are injured by the forma- 

 tion of ice at temperatures which they can withstand if 

 the formation of ice is prevented. Again, some plants 

 are not injured if the formation of ice does not progress 

 too far, while some are resistant to the lowest tempera- 



tures. As yet we do not know the nature of the peculi- 

 arities which determine the different powers of resist- 

 tance of individual plants or of the same plant at 

 different stages of growth. It is well known that the 

 resistance to injury can be increased to a certain extent 

 by raising the concentration of the cell-sap. Cold, in 

 itself, acts as a stimulus, inducing an increased produc- 

 tion of sugar in many plants. The presence of an 

 increased amount of sugar in a plant acts in such a way 

 as appreciably to lower the freezing-point While tables 

 giving injurious temperatures to fruit when in bud, 

 blossom, and so on, have been prepared, it is safe to say 

 that these temperatures are not entirely reliable. This 

 is because conditions are never the same in any frost 

 period. It may be stated that in the practice of orchard- 

 heating the safest plan is to keep the temperature just 

 above the freezing-point no matter what the variety 

 of fruit. No doubt, this will often be 2 to 3, or even 

 more, higher than necessary, but the practice is on the 

 safe side. In orchard-heating practice the temperature 

 should never be allowed to go much below the danger 



point, as it is usually 

 difficult to bring it 

 back without some 

 chance of injury to 

 the fruit. 



Effect of orchard- 

 heating on pollination. 

 That pollination 

 and subsequent fertil- 

 ization of the orchard 

 fruits is in any way 

 affected by orchard- 

 heating is yet to be 

 proved. It has been 

 contended by some 

 that the smoke or 

 soot incident to the 

 use of fuel-oil has a 

 tendency to prevent 

 the normal activities 

 of such insects as visit 

 the blossoms of fruit 

 trees. However, there 

 is no proof that the 

 presence of soot on 

 the trees has any 



effect in keeping insects, especially the honey-bee, away 

 from the newly opened blossoms. Under normal con- 

 ditions, the blooms which bees visit open during the 

 early part of the day and, therefore, only such blossoms 

 attract them. These blossoms have been closed during 

 the time when smudging was being done, and, therefore, 

 the nectaries, pistils and stamens have no soot deposited 

 upon them. With citrus fruits, soot may have an inju- 

 rious effect upon the fruit, but it has been found that 

 such fruit may be freed from soot by a washing process 

 which does not materially increase the cost of handling. 

 The cost of orchard-heating. The cost of orchard- 

 heating is such a variable quantity that it is almost 

 impossible to make a general estimate which will be 

 of any value. Equipment, cost of fuel, length and 

 number of firing periods, and so on, will vary in differ- 

 ent localities and seasons. Orchard-heaters will cost 

 all the way from 6 cents to 50 cents each, and from 

 fifty to two hundred heaters, depending upon condi- 

 tions, will have to be used to the acre. The quantity 

 of oil will vary with the season, and the cost will be 

 all the way from 1 to 5 or 6 cents a gallon. Usually, 

 no less than 300 gallons an acre should be provided. At 

 least one wagon-tank will have to be provided for each 

 10 acres at a cost of $25. Lighters and torches will 

 cost from $1 to $2 an acre; thermometers 75 cents to 

 $1 an acre. The cost of a storage- tank charged to each 

 acre will depend upon its size, but will not be far from 

 $10 an acre for large tracts. It is possible to get at the 



