198 CITRUS FRUITS AND THEIR CULTURE. 



consequently the flavor. Not all of these effects are notic- 

 able in all varieties and only here and there are they suf- 

 ficiently marked to attract attention. But if differences 

 stand out prominently here and there, it is not unreason 

 able to suppose that they exist in some degree in many 

 other instances to which attention has not been directed. 



SOUR ORANGE (C. VULGARIS). 



Next to the trifoliate orange, the sour is the hardi- 

 est of all the varieties or species of citrus trees used as 

 stocks. As compared with C. trifoliata, it is not nearly 

 so hardy, but it is considerably hardier than the sweet 

 orange. Of course, a very low temperature causes all 

 differences in hardiness between sweet and sour orange 

 trees to disappear and after such periods of cold no dif- 

 ference can be detected, but the fact remains that a degree 

 of cold which frequently injures the sweet orange has 

 no effect on the sour. Sufficient cold to destroy the young 

 growth and defoliate sweet orange trees does little or no 

 injury to the sour orange. It is impossible to state the 

 relative hardiness in so many degrees, as so much depends 

 upon the condition of the trees, 



The roots of the sour orange are produced abundantly 

 and penetrate well into the soil. In this respect it pos- 

 sesses an advantage over the sweet stock for some dis- 

 tricts in that it is not so readily affected by variations 

 in moisture. The roots penetrate sufficiently deep to be 

 in contact with a more or less permanent water supply. 



Sour orange stock is not subject to the attacks of 

 mal-di-goma, and in Europe where this disease worked 

 great havoc years ago, the groves have again been built 

 up by using sour orange stock. On soils subject to the 

 disease it is a safe stock to use. The sour orange tree is 



