CITRUS CULTURE IN CALIFORNIA — POLLINATION. 23 



than farther north, where this range is practically unbroken 

 and the citrus belt is farther inland. These disadvantages of 

 the northern section are, however, somewhat counteracted iu the 

 fact that the drier and warmer summer atmosphere is a greater 

 guarantee against the spread and ravages of insect pests. The 

 more elevated and inland localities in the south have this same 

 advantage over localities nearer the coast. 



There are orange and lemon trees growing in nearly all of 

 the counties of the State not exclusively' in the mountainous 

 sections, and many of these trees are bearing more or less fruit 

 of very fair quality. For climatic reasons, however, the citrus 

 fruit industry is and must be confined to a belt of country 

 ij'ing along the foothills of the Sierra Nevada Mountains. 

 This belt is called the " Thermal Belt." It stretches from San 

 Diego to Tehama County, a distance of over seven hundred 

 miles, and varies in width from three or four miles to twenty- 

 five or thirty. In this belt it is estimated there are about 

 1,500,000 acres of land adapted to the safe cultivation of citrus 

 fruits on a commercial basis. 



The altitude ranges from 30 to 1,800 feet above sea-level. 

 The mean summer temperature of this belt is somewhat higher 

 in the northern portion than in the southern, but the mean 

 winter temperature is higher in the southern than in the 

 northern portion. The mean temperature for the year does 

 not vary more than four degrees throughout the whole belt. 



POLLINATION-HYBRIDS. 



The mixing of the pollen among the flowers of the species 

 has given birth to innumerable hybrids, distinguished as such 

 and designated as varieties, by their remaining constant, i. e., 

 not reverting to the mother type after continuous propaga- 

 tion. With the constant multiplication of varieties it would 

 be difficult to trace to what species many hybrids belong. 

 Many partake of the lemon, the orange, and the citron. 



The flower of the orange is nothing but a transformed 

 branch, coming out of either the axilla of an ordinary leaf or 

 from that of an abortive leaf, usually called a bract. This 

 transformed branch, or flower, in the orange, consists of sev- 

 eral whorls or transformed leaves, viz: the calyx whorl, the 



