8 The Principles of Fruit-growing. 
type or group of fruits; but in general it may be 
said that the relative annual temperature is the 
most influential factor. 
The temperature determinunit.— It is customary to 
recognize three general  c¢limatal fruit-zones,—the 
temperate (typified by the apple and the peach), the 
semi-tropical (eitrous tribes, fig, olive, pomegranate) , 
and the tropical (cocoa-nut, banana, anona, mango). 
There are no positive limits of temperature which 
mark off or separate these zones; but it is enough 
for our purpose to say that the temperate zone is 
one which is marked by a long winter of freezing 
and by the deciduous types of fruits; the semi- 
tropical zone is one in which the winter is a short 
season of light frosts or only occasional freezes, and 
in which the fruit trees are evergreen or very nearly 
so; and the tropical zone is frostless, and is marked 
by evergreen and mostly ever-growing fruit-plants. 
The lunits of these climatal zones ave exceedingly 
devious. In eastern North America, the northern 
limit of profitable fruit-growing is not far from the 
forty-fifth parallel, and the limit sinks considerably 
lower than this in -the middle west, and rises mueh 
above it on the Pacific slope. The northern mit 
of the sub-tropical zone in the east is Northern 
Florida and a narrow area skirting the Gulf of 
Mexico, and upon the western side of the continent 
it extends in the valley climates as high as the 
fortieth parallel. The only portion of the tropical 
fruit-zone which les in the United States is in 
extreme southern Florida, comprising about two 
