ORCHARD LOCATIONS AND SITES 



653 



The magnitude of such disparities often found between points on the 

 same farm and occupying positions differing Uttle in elevation or exposure, 

 is not appreciated. Their influence is often subtle, but nevertheless real. 

 They may make the difference between the necessity of one or of three 

 applications of a fungicide, an interval of a week in the time of partic- 

 ular spray applications, or of a week in the blossoming or maturing seasons 

 of a fruit. 



Temperature. — It is not the intention in this discussion to present 

 further data on the influence of a certain number of "heat-units" in 

 bringing to particular stages of maturity plants of different kinds. 

 However, mention may be made of the variation in the mean temperature 

 between stations only a short distance apart. MacDougaH^ presents 

 data showing that, of two stations in the New York Botanic Garden only 

 a few hundred yards apart and presenting no great difference in elevation, 

 one received 78,836 hour-degrees of heat in 1 year and the other only 

 68,596. One of these points registered a temperature below freezing 

 during 1478 hours in the course of the year and the other during 1736 

 hours. Here is a difference of 13 per cent in heat units; in other words, 

 one station enjoyed a temperature that was equivalent to an active grow- 

 ing season of about 11 days longer than the other. Such a disparity is 

 large enough to account for the difference between success and failure 

 with many fruit crops, as for instance grapes, along the northern limits 

 of their cultural range and it shows the importance to the grower of study- 

 ing carefully the local variations often found within the limits of a single 

 farm. 



Equally or even more striking are the figures recording the temper- 

 atures of two stations on the campus of the University of California at 



