274 DOMESTICATED ANIMALS AND PLANTS 



any considerable length of time, and would soon become extinct 

 were it not constantly renewed. Whether the apricot is a mu- 

 tant from the plum, or the reverse, we could now only speculate, 

 but from general reasoning we should regard the apricot as the 

 original stock and the plum the mutant. 1 



The orange and the lemon. These two popular tropical fruits 

 belong to a tangled group covered by the generic name Citrus, 

 and including also the lime and the shaddock. While their 

 original has not been identified in the wild, their origin is uni- 

 versally credited to eastern Asia, probably China. The principal 

 strains of this genus are as follows : 



The citron {Citrus medica proper), a large nonspherical fruit 

 with an aromatic rind and a moderate amount of not very acid 

 juice. 



The shaddock, or grapefruit {Citrus decumana), large and 

 round, juicy, slightly acid, extensively cultivated in southern 

 Asia and in the tropics generally. 



The lemon {Citrus medica limonum), juice decidedly acid. 



The lime {Citrus medica acida), like the lemon, but much 

 smaller ; juice very acid. 



The orange {Citrus aurantium), in two varieties, bitter and 

 sweet, of which the latter is the cultivated, and of which the 

 tangerine and the mandarin are minor strains distinguished by 

 the easily separated rind, and for this reason often called " kid- 

 glove oranges." 



The citrous fruits have a pronounced acid quality and a lurking 

 tendency to be bitter, a tendency that crops out strongest in the 

 bitter orange, which is wild, and in the shaddock, which is culti- 

 vated. 2 These fruits have been long in cultivation, as fruits go, 



1 This is because the mutant is more commonly destitute of some character 

 that is present in the original. Nearly every pubescent species, too, has its 

 smooth variety, which in some cases succeeds better than the original. The 

 fact that we do not see the mutation is no argument that it has not taken 

 place. Plain wheat, for example, has certainly arisen from the bearded, which 

 is to be regarded as the original stock. See further in the chapter on Mutation. 



2 It may be added that the common orange easily escapes from cultivation, 

 in which case most of the trees bear insipid fruit, a few bitter, and occasionally 



