FRUIT BREEDING 277 



chromosome pairs. In heterozygous material, however, new 

 combinations of factors would be produced which might cause 

 changes in the external appearance of the organism. No cyto- 

 logical basis for such cross-overs has been demonstrated. 



Controlled Crosses. One of the earliest controlled experi- 

 ments in the breeding of fruits by crossing was started by Swingle, 

 in 1893, in Florida. This was an attempt to produce hardier 

 types by the use of wild citrus species. The hardy Chinese species, 

 Citrus trifoliata, was used as one of the parents. In 1897, 212 

 crosses were made between this species and orange varieties. 

 The three fruits that were produced gave thirteen hybrids, which 

 were so different from existing varieties of citrous fruits that 

 they were called "Citranges." Other crosses between citrous 

 species were made. One of the promising combinations was a 

 cross between the West India lime and the kumquat orange. 

 This orange is one of the hardiest of the evergreen citrous trees 

 while the lime is very tender. Further experiments are under 

 way and other promising wild relatives of the citrous fruits have 

 been obtained. Crosses of this nature are producing fruit varie- 

 ties which are successful in regions where citrous fruits could 

 not be grown formerly. The work shows the necessity of a 

 thorough botanical knowledge of the wild relatives of the crop 

 which it is hoped to improve by breeding. 



A somewhat similar method of work with the hope of producing 

 hardy apples for the Canadian Northwest was started by William 

 Saunders in Canada in 1888. The wild Siberian crab, Pyrus 

 baccata, which proved hardy on the prairies and withstood 

 temperatures of 50 below zero, was used as the female parent and 

 crossed with commercial apple varieties. Macoun (1915) states 

 that the fruit of Pyrus baccata averages % in- in diameter and is 

 quite astringent. The fruits obtained from some of the more 

 promising ol the crosses were not so large as desired, although 

 some compared very favorably in size with ordinary crabs. 

 They were of good flavor and proved hardier than any varieties 

 of apples and crabs that had been tested up to that time. Several 

 are here listed. 



Jewel, P. baccata X Yellow Transparent. Size 1.4 by 1.3 in. 

 Columbia, P. baccata X Broad Green. Size 1.8 by 1.6 in. 



Charles, P. baccata X Tetofsky. Size 1.6 by 1.5 in. 



Recrosses between the best of these and apple varieties were 



