6 BT^TT.F.TTN- 821, U. S. DEPAETMEI^T OF AGEICULTLTRE. 
A number of otlier factors are of even greater consideration than 
tlie immediate injnry 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 u;ed in orchard heaters. A large supply of oilis 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 pum.ped, 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. 
