264 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



It has been supposed that lemons can withstand a temperature of 

 28 F. without injury, but whether the crop of small fruit can be 

 exposed to this temperature without loss has never been determined 

 with sufficient accuracy to be convincing. The tendency among the 

 best orchardists is to regard any temperature below 32 F. as 

 dangerous.* 



Lisbon fruit was less easily damaged than that of Eurekas. The 

 difference did not seem to be due entirely, at any rate, to the heavier 

 foliage of the Lisbons, because the fruit of the heavy foliage type of 

 Eureka was injured more than the Lisbon fruit. 



Yellow or tree-ripe lemons were more sensitive to frost injury than 

 either the large-sized silver or green fruit. The packing-house reports 

 from one young grove showed practically no loss of the large-sized 

 green fruit, and only 15 per cent frozen fruit in the silver ; while the 

 tree-ripes were a total loss. This comparative resistance between the 

 yellow or tree-ripe and the green fruit was found to be quite general. 



NATUEAL FACTOES INFLUENCING THE TEMPEEATUEE 



Elevation. Comparative elevation is a very important element in 

 influencing temperature. It was common to hear people remark, soon 

 after the freeze, that it was colder this year on the higher levels than 

 it was on the lower ground; but this was not generally so. Investi- 

 gation showed that as usual the lower portions of most districts were 

 colder than the higher land of those districts. There were many 

 places where this advantage of the higher ground was clearly illus- 

 trated in a single grove. In such groves a gradual transition could 

 be seen from the uninjured fruit and foliage of the higher portions 

 to entirely defoliated trees below. 



It must be understood that it is, in all cases, the relative elevation 

 that is important, not the actual elevation above sea-level. An ad- 

 joining low area, valley, or arroyo that afforded opportunity for the 

 cold air to drain off was in this freeze, as in other freezes, of decided 

 advantage. 



There were some places, nevertheless, where, contrary to the rela- 

 tions existing in most years, the damage on the higher ground was 

 greater than farther down the slope. In Upland this was shown by 

 the condition of the street trees, the pepper trees at the top of the hill 

 being defoliated and those lower down showing only slight damage. 



* Compare article on ' ' Eeeent Investigations in Orchard Heating, " by I. G. 

 McBeth and J. E. Allison, The California Citrograph, January, 1919, p. 51. 



