THE GEOGRAPHY OF FRUIT GROWING 621 



fruits of its more northern reaches are the pecan, the muscadine grapes 

 and pears of the oriental hybrid class. The Lower Sonoran area is 

 characterized by many cacti, yuccas, agaves, mesquites and other desert 

 plants. It produces plums, prunes, peaches, cherries, apricots, almonds, 

 grapes and many other fruits in great quantities where irrigation water is 

 available. The southern part of the Lower Austral zone is known to the 

 pomologist as the Subtropic zone. Horticulturally it is one of the most 

 important in the United States. Within it are produced citrus fruits, 

 figs, avocados, loquats, Japanese persimmons and many other less 

 known fruits. 



Attention may be directed to the fact that the boundaries of the 

 pomological districts of the United States, as they have been mapped by 

 the American Pomological Society do not coincide exactly with those of 

 the life zones that have been discussed, though the two maps have many 

 features in common. 



GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY TEMPERATURE 



It will be noted that these life zones or crop zones include areas charac- 

 terized by a certain uniformity of climate and that, of all the features 

 that constitute climate, temperature is given first consideration. Indeed 

 the boundaries of the different regions and zones are for the most part 

 isothermals, and the main reason for such irregular outlines, especially 

 in the mountainous districts, is the influence of altitude upon temperature. 

 High altitude through its accompaniment low-temperatur, accounts for 

 the island-like areas of the Boreal or Transition zones in latitudes gen- 

 erally dominated by the life of the Austral. Generally there is a lower- 

 ing of about 4°F. in mean temperature for each increase in elevation 

 of 1,000 feet. Even at the equator frost will occur at an elevation of 

 about 18,000 feet; on the island of Hawaii, at a latitude of 20° North, 

 frost occurs at an altitude of 4,500 feet or above. ''^ 



Temperature here is meant to include • not only the mean annual 

 temperature but also the minimum and maximum temperatures of 

 winter, spring, summer and autumn, respectively, the mean temperature 

 month by month, particularly through the growing season, the occurrence 

 of frost during the critical period just before, during and just after, 

 blossoming, the length of the growing season (see Fig. 66), the evenness 

 of temperature from day to day, and many other characteristics of the 

 weather that are more or less directly attributable to temperature 

 changes. Sometimes it is one of these features of temperature, e.g., 

 minimum winter temperature, or mean temperature during the growing 

 season, that sets the limits for a certain fruit; sometimes it is another. 

 Broadly speaking it is the minimum winter temperatures that set northern 



