142 PROCEEDINGS OF THIRTY-SIXTH FRUIT-GROWERS ' CONVENTION. 



remained at about 20 c F. from 3 to 8 a. m. December 2Lst. This was 

 the coldest weather in this locality since 1888. It is evident that in 

 this case a large amount of heat was lost. 



Many small fires are much more effective than a few large fires. In 

 the use of numerous small heating devices, it is possible to distribute 

 the heat where it is most needed. It is also possible by increasing the 

 number of wire baskets, oil pots or orchard heaters to offset a con- 

 tinuing fall in temperature. It should, however, be stated that with 

 most oil pots, unless the combustion is excellent, there is a deposit of 

 soot which may settle on the fruit. 



Under the second head, that of saving heat, we have all the various 

 smudging devices for artificial cloud making and all the different forms 

 of covering. The object, of course, is to utilize the earth's heat as much 

 as possible by entrapping it. Any cover spread above the ground inter- 

 feres with loss by radiation ; and the most effective protective methods 

 have rightly been based upon this saving and storage of heat. To be 

 thoroughly effective, however, the cover should be spread before the 

 earth has lost most of its heat. This is the fault of most smudging 

 efforts; namely, that they are begun too late. The cover, or shield, 

 has another advantage in that it serves after sunrise as a guard against 

 the too rapid warming of the chilled plant after sunrise. We have 

 examined many orchards in California and found that fruit was most 

 damaged where exposed to the direct rays of the sun. While it is not 

 definitely known what action causes the death of the cell, whether it 

 be a rupture of the cell walls or a separation of the water and absence 

 of the necessary turgidity. it would seem that we could not err in 

 guarding the plant fiber from strain due to rapid and unequal heating 

 while still chilled. 



Of the various forms of cover devices, the lattice work is probably 

 the most expensive; but certainly the most effective. 



A new form of cover, known as an anti-frost cover, was devised last 

 year in the San Francisco Weather Bureau office. It is, however, 

 better suited for the protection of small fruit, garden flowers, and 

 vegetables. It is an old and widely known practice to cover garden 

 flowers with newspapers when frost is expected. In the new anti-frost 

 cover there is used instead of a single cover a double layer of prepared 

 paper with an intervening air space. This prevents almost perfectly 

 the escape of the long heat waves from the ground. Such covering can 

 be spread above the plant an hour or two before sunset, i. e.. before 

 the ground has lost much of its heat. If at the same time shallow pans 

 of warm water are placed under the cover, an effective screen and serv- 

 iceable supply of water are provided. It is also to be noted that we 

 use this cover at a time when the roots are absorbing vigorously and 

 transpiration by the leaves is at a maximum. We. therefore, prevent 

 any lowering of temperature at the leaf surface and store up in the 

 plant a quantity of heat energy for expenditure slowly through the 

 night hours. The actual temperature of the air is of less importance 

 than the temperature of the leaf or fruit surface. A deposit of 

 moisture is advantageous. 



A special use of the anti-frost cover in connection with tree fruits is 

 to unroll the covers in the orchard before sunset and to roll them up 

 about 4 o'clock in the morning. 



