FROST PROTECTION IN LEMON ORCHARDS. 
Adequate provision was made in all the protected orchards in 
which these studies were conducted for refilling the heaters from, 
storage reservoirs, such as the one shown in figure 4, and for their 
continuous care during the frosts. One of the methods used for 
distributing the oil is shown in figure 5. It can be safely said that 
in the orchards under observation the maximum efficiency of the 
heaters was obtained during the cold periods. 
OBJECTS OF THE INVESTIGATIONS. 
The effect of the low temperatures upon the lemon trees in non- 
heated orchards was very noticeable immediately following the freeze. 
The trees in non- 
heated orchards were 
partially or com- 
pletely defoHated, as 
shown in Plates I 
and II. The trees in 
heated orchards did 
not show this con- 
dition to any marked 
extent except in the 
upper branches, 
where the leaves were 
blown off by the 
violent winds which 
accompanied the low 
temperatures, as 
shown in Plate III. 
In the nonheated or- 
chards in many in- 
stances the bark on 
the branches and, in 
some cases, on the 
trunk of the trees, 
was split more or less 
severely. Often it 
was necessary to cut 
off these injured branches during the spring months following the 
low temperatures, in order to aid the trees in recovering from frost 
injury. In nearly all cases where trees were defoliated it was 
found desirable to whitewash the trunks and main branches, in 
order to protect the trees from further injury by exposure to the sun. 
It was therefore possible, in a general way, to determine the amount 
of immediate injury to the trees themselves. 
Fig. 3.— Heaters in position for use in a Corona lemon orchard. The 
heaters are usually set on a small board or other support in order to 
avoid as far as possible damage from rust due to contact Avith the soil. 
Great care must be used in order to prevent leakage from the heat- 
ers, as even small quantities of oil in orchard soils have been found to 
be injurious to the trees. As soon as the cold weather is over, the pots 
are usually removed from the orchard, emptied, cleaned, coated with 
hot oil, and stored for the summer. 
