On the Northern Limit of the Distribution 

 of Citrus trifoliata in Japan. 



By 

 Prof. Dr. M. Shirai. 



Citrus trifoliata, in Japanese " Karatachi ", meaning Korean 

 citrus, is not indigenous to Japan but is cultivated from ver}' 

 ancient times. It is already mentioned in the oldest hymn-book 

 " Manyo-waka-shu " (MMfatytifk) > compiled in 759 A. D. The 

 tree is noted for its hard}' character and is commonly used as 

 hedges and grafting-stocks of citrus plants. Until recently no 

 other Uses have been invented than that mentioned above, when 

 American naturalists attempted to utilize the plant in making 

 hardy hybrids of citrus fruits. 



An account of the successful results of this new enterprise 

 may be found in Professor Bailey's Plant Breeding, which runs 

 as follows : 



" Work on the production of frost-proof types was started 

 first in 1893-1894, but the hybrids were lost by accident other 

 hydrids were made in 1896 and 1897. A study of the possibilities 

 in this direction indicated clearly that if any great advance was 

 to be made, it would probably come through hybridation. For 

 very many years, growers had been carefully watching for hardy 

 variations, and among the many thousands of seedlings grown 

 in Florida and other countries where freezes occur occasionally, 

 such hardy variations, if there were any, would have been 

 noticed and utilized. '1'he Department sought to produce hardy 

 types by combining the hardy but worthless trifoliata orange 

 (Citrus trifoliata) with the common sweet orange, hoping to 

 secure hybrids having the hardiness of the trifoliata and the 

 edible fruits of the common orange. 



'The hybrids were found to vary greatly in the firsl gem 



