6 BULLETIN 821, U. S. DEPAETMEISTT OF AGKICULTUEE. 



A number of other factors are of even greater consideration than 

 the immediate injury to the trees. In order to secure definite infor- 

 mation concerning these factors, the investigations discussed in this 

 bulletin were undertaken. The objects of these investigations were 

 (1) the determination of the effectiveness of orchard heaters, as 

 measured by the number, commercial quahty, and value of the fruits 

 produced by lemon trees in orchards protected by oil heaters and in 

 comparative unprotected orchards, (2) the determination of the 

 length of time it took trees in orchards which were not protected 

 with heaters to return to normal production, (3) the determination 

 of the behavior of lemon trees in heated and nonheated orchards the 



Fig. 4.— Cement reservoir for the storage of oil used in orchard heaters. A large supply of oil is stored 

 in this tank to be used for refilling heaters during periods of low temperature. The reservoir is 

 arranged so that the oil can be carried by gravity through pipe lines to various sections of the or- 

 chard, or the oil can be pumped, if necessary, directly into tank wagons for distribution to the 

 heaters. 



second year after the freeze, and (4) a comparison of the frost injury 

 in orchards of both Eureka and Lisbon lemon trees, which are the 

 two important varieties grown in California. 



On account of the fact that previous to the freeze no tree records 

 had been kept in the comparative heated and nonheated orchards 

 under observation it is not possible to show the behavior of the trees 

 in these orchards prior to 1913. However, all plats were located in 

 orchards where the conditions were as nearly comparable as possible. 



The object of this pubhcation is not to cover the subject of frost 

 protection, but to submit data which shows the actual behavior of 

 trees in protected and unprotected lemon orchards in one district of 

 southern Cahfornia for the two years following the freeze of January, 

 1913. 



