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THE AMERICAN NATURALIST [Vol. XL VIII 



assumed, in respect to these differential characters, to be pure; 

 or, expressed in more technical language, each species is for the 

 characters under observation, genotypically homozygous. This 

 assumption is based on wholly inadequate evidence, as will be 

 shown later. 



Citrus trifoliata crossed with other Citrus species (C. auran- 

 tium, etc.) gave F x hybrid families showing a large degree of 

 variability, even when the seeds from a single cross having 

 identical male and female parents were grown. This variability 

 expressed itself in foliage, habit of growth, and fruit, and was 

 especially noticeable in the latter, the fruits of the F, individuals 

 showing differences in color, size, texture, shape, number of seeds, 

 and flavor. For example, from a single cross of C. trifoliata X C. 

 an rant iu m. the 11 resulting hybrid seeds gave rise to F x plants 

 (citranges) differing in foliage, habit of growth, and very strik- 

 ingly in fruit. The fruit of one of these citranges, the "Morton," 

 was smooth, round, very large, and orange-colored ; those of the 

 "Colman" were rather flattened, globose, pubescent, yellow, al- 

 most seedless, and lacked the disagreeable oil common to the 

 others; while those of still another type, the "Willits," were 

 often monstrously fingered. The "Phelps" was bitter, while the 

 "Saunders" almost lacked this quality. The "Rustic" often has 

 double fruits with many seeds, and a habit of growth more like 

 its aurantium parent. 



When varieties of the lemon were crossed with C. trifoliata, 

 still greater differences in the F, generation (citremons) resulted. 

 These consisted largely of "abnormal" foliage developments. 

 Hypophylls, though absent in the common Citrus species are ex- 

 tremely characteristic of C. trifoliata. About 20 per cent, of the 

 lemon-trifoliata hybrids developed an intensified form of this 

 character, and this proportion occurred in each case in crosses 

 involving three different varieties of lemon. The tangerine 

 orange X grape fruit (tangelo) in the F t generation was almost 

 as variable as the citrange families. F x hybrids between the 

 West Indian lime and the kumquat (limequat) were strikingly 

 different in such characters as aroma, flavor, acidity of pulp and 

 thickness of skin. 



Although much stress has been laid on the differences in these 

 F x hybrids, there were numerous similarities. For example, all 

 the Citrus hybrids involving C. trifoliata in their parentage have 

 compound, semi-evergreen leaves, increased hardiness and fruits 



