THE GEOGRAPHY OF FRUIT GROWING 631 



GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY RAINFALL AND 



HUMIDITY 



Of hardly less significance than temperature is the influence of humid- 

 ity in determining the limits of life and crop zones and in the geography 

 of fruit growing. By humidity is meant here total rainfall, distribution 

 throughout the season, availability for plant growth and atmospheric 

 humidity. Only in countries or districts where the topography leads to 

 marked differences in rainfall between points close together and enjoying 

 practically the same temperatures are the full effectsof humidity strikingly 

 brought out. Thus " . . .at one of the substations of the United States 

 Experiment Station on the Island of Hawaii, a rainfall of 360 inches was 

 recorded for 1 year, while at a point 28 miles away the annual rainfall for 

 the same year was 6 inches. It is possible ... in the space of an hour's 

 ride to pass from a desert covered with cacti and other drought-resistant 

 plants into a dense tropical jungle reeking with moisture." ^^ 



For the most part fruit trees thrive better in a fairly humid climate, 

 a fact shown by the natural distribution of their undomesticated relatives. 

 Many species, however, like the date palm and olive, succeed in a very 

 arid climate. Some of the great variations in the actual water require- 

 ments of different kinds of fruit are shown by data presented in the sec- 

 tion on Water Relations. Often different varieties of the same kind 

 of fruit vary considerably in water requirements. The Yellow Trans- 

 parent apple will thrive and produce good fruit on less water than the 

 Winesap or York. Certain varieties or types of dates are grown at 

 Alexandria, Egypt, where the mean atmospheric humidity is from 64 to 

 72 per cent, while certain other varieties are grown in some of the desert 

 oases having an atmospheric humidity of only 34 per cent. Those varie- 

 ties that thrive under the one set of conditions, however, cannot be grown 

 successfully in the other environment.^^ As these humidity requirements 

 of different fruits become known it is possible to draw, more or less accur- 

 ately, iso-hyetal lines setting approximate boundaries for districts in 

 which they may be expected to reach a high degree of development. 



Data presented in Table 8, however, show the danger in placing too 

 much reliance upon rainfall figures as an index to fruit crop or varietal 

 adaptation. Thus Fitchburg, Mass. has a mean annual rainfall of 45.4 

 inches, 28.6 coming during the growing months, while Missoula, Mont., 

 has a total precipitation of only 15.5 inches, of which 10.4 comes during 

 the growing months; yet both are apple growing centers and Mcintosh 

 is one of the most satisfactorj^ varieties in both places. Irrigation, how- 

 ever, is employed in Montana. Vineland, N. J., has an annual rainfall 

 of 47.3 inches, three-fourths of which falls during the growing season; 

 yet The Dalles, Ore., with less than one-third of that total rainfall and 

 with only one-sixth as much falling during the growing season as comes 

 during the corresponding period in New Jersey, produces peaches and 



