654 FUNDAMENTALS OF FRUIT PRODUCTION 



Berkeley, presented in Table 14. Though these stations were 120 feet 

 apart in elevation, elevation alone cannot be held responsible for the 

 differences recorded, for, as mentioned elsewhere, the influence of ele- 

 vation on mean temperature amounts to only 4°F. for each 1000 feet. 

 Without doubt many factors contribute to these local variations in tem- 

 perature, some being more important in one case and others in another. 

 It is not so important that all these factors be known and exactly evaluated 

 in every instance as it is that their combined effect be recognized and 

 properly utilized. 



Evaporation, Rainfall and Other Factors. — It is generally recognized 

 that some spots or some locations are more subject than others to the 

 drying action of the wind; however, the extent and importance of differ- 

 ences in this respect are not generally recognized. Gager^^ records results 

 of evaporimeter experiments in the New York Botanic Garden in 1907 that 

 are particularly interesting. Three specially constructed evaporimeters 

 were placed at several points in the garden ; one was on a dry rocky knoll 

 partly shaded by trees; a second was on low, poorly drained, marshy 

 ground, also partly shaded and the third was in the open on well drained 

 ground with sod on the one side and cultivated ground on the other. The 

 evaporation losses from these different instruments between June 3 and 

 October 14 were equivalent to 8.47, 4.84 and 12.10 inches, respectively. 

 The precipitation during the same period was 9.32 inches. At the first 

 station precipitation exceeded evaporation loss by only 0.85 inch, at the 

 second station by 4.48 inches, while at the third station the evaporation 

 loss exceeded precipitation by 2.78 inches. In commenting on these 

 data, Gager says: "It should be kept in mind that the loss of water 

 from the evaporimeters is not a measure of the amount of water lost by 

 the soil through evaporation, but it is only an index of the evapor- 

 ating power of the air for the given station. For the same locality the 

 rate of evaporation from soil and from evaporimeter will materially 

 differ, being less from soil and varying with its nature and condition, as 

 well as with the surroundings above the soil surface." Nevertheless at 

 one station the evaporation losses were between two and three times those 

 at one of the others and such a difference may often be enough to have a 

 great influence on plant growth and crop yield. 



Local variations in rainfall are likely to be especially large in sections 

 showing considerable difference in elevation, but they are often important 

 where the elevations are substantially the same. Thus at Davis, Cali- 

 fornia, when the annual rainfall was 16 inches, it was about 25 inches at 

 a point ten miles to the west and having the same elevation. Thirty 

 miles still further west, but in the foothills of the Coast Range, it was 

 over 50 inches. 



With the local variations in temperature and humidity there are often 

 important differences in the prevalence of insects and diseases that., 



