204 CITRUS FRUITS AND THEIR CULTURE. 



regions of imparting to many varieties worked upon it, 

 some of its own hardiness. While it should be borne in 

 mind that the point of union between the stock and cion 

 is the one point in the trunk of a citrus tree most sensi- 

 tive to cold, still this point of union may be protected 

 and thus a distinct gain in ability to withstand low tem- 

 peratures is made. Besides imparting to the cion some 

 of its ability to withstand cold, it has a tendency to 

 retard growth in spring. C. trifoliata has been known 

 to withstand a temperature below zero, a temperature 

 sufficiently low to establish the claim that it is not in- 

 jured by severe cold. This claim would be worthless, how- 

 ever, were it not distinctly periodic in its growth and, 

 moreover, it is not responsive to sudden changes of temper- 

 ature during the dormant period. 



As a general rule those trees which reach their max- 

 imum development in cold or comparatively cold climates 

 cannot be transferred to distinctly tropical or sub-tropical 

 climates and there grown successfully. Now, since the 

 trifoliate orange succeeds admirably and appears to be 

 well adapted to regions distinctly outside the tropical 

 isotherm, it is doubtful whether it is advisable to use it 

 as a stock in regions removed from all effects of frost. 

 In view of this fact, it would be unsafe to recommend 

 it as a stock for use in the Islands, and on the whole it 

 is safest to use it only in the colder regions. In southern 

 California it is not likely to prove satisfactory, except at 

 comparatively high altitudes. It has proved quite satis- 

 factory in northern Florida and also in Louisiana and 

 Texas. 



The trifoliate orange should not be used as a stock 

 on high, dry or calcareous soils. For such situations, it 

 is a failure. It grows well and vigorously on good flat 



