FROST PROTECTION IIT LEMON ORCHARDS. 7 
PLAN OF THE INVESTIGATIONS. 
The investigations discussed in this bulletin were one feature of a 
general study of the effect of frost injury on citrus fruits conducted 
by Dr. H. J. Webber, Director of the Citrus Experiment Station of 
the University of California, at Riverside, his associates, and the 
writers. A report on certain phases of the studies has been pub- 
lished by Webber and others.^ Only a brief abstract of the 
investigations discussed in the following pages appears in the 
above-mentioned report. 
Owing to the fact that frost injuries frequently vary in degree in 
the same orchard, due to such local conditions as the lay of the land, 
care was used in the selection of the comparative heated and non- 
heated plats, so that they were practically identical with respect to 
Fig. 5.— Tank wagons used for distributing oil to empty heaters. These provide means for quickly 
filling the empty heaters during periods of continued low temperature. Some of the orchards are 
fitted with pipelines which distribute the oil to different sections. 
the influence of low temperatures and other cHmatic conditions. A 
committee, which included Dr. Webber, four prominent citrus grow- 
ers, and the writers, made the selection of the plats and agreed upon 
their adaptability for the purpose of this study. In every case the 
comparative orchards were very near together, usually adjoining 
groves, and at the same altitude. The trees were about the same, 
age — 20 years — so that differences in production could not be 
attributed to any marked difference in the age of the trees. After 
a careful survey of the orchards the trees for the comparative plats 
were selected with a view to insuring fair and comparative conditions. 
1 "Webber, H. J., and others. A study of the effects of freezes on Citrus in California. Cal. Agr. Exp. Sta. 
Bui. 304, p. 243-321, 22 fig. 1919. 
