No. 567] SHORTER ARTICLES AND CORRESPONDENCE 187 



with abundant bitterish, acid juice. Two of the citranges (Col- 

 man and Cunningham) have the pubescent fruit character of 

 C. frifoliata, while the others are smooth-skinned. 



The author's data led him to formulate in substance the follow- 

 ing conclusions, which I have grouped and stated in my own 

 language. 



1. Citrus species are but slightly variable in the characters 

 which differentiate them, and, in the sense that no overlapping 

 takes place, may be said to breed true, their germ cells being 

 genetically pure for these differential characters. 



2. Individual plants of the F x hybrid generations between these 

 species are strikingly variable, although all are, in a given cross, 

 the zygotic product of pairs of gametes of "identical hereditary 

 composition." 



3. Modern theories of heredity can not account for this varia- 



These are not the conclusions, however, in which all present- 

 day geneticists would concur. In the first place, few "modern" 

 geneticists would take Swingle's view concerning the "pure 

 breeding" ability of the various Citrus species, nor even of C. 

 aurantium. Webber, in the Encyclopedia of American Horti- 

 culture, notes that 70 varieties of the common sweet orange are 

 grown within our borders, and although a few varieties are 

 fairly constant, the majority of these do not breed true from seed. 

 Practically the same idea has been gained by certain prominent 

 taxonomists of the genus Citrus. De Candolle specifically calls 

 attention to the remarkable variability of the whole group ; and 

 Professor Hume of Florida remarks on the same fact in certain 

 Experiment Station publications. As to the variability among 

 the individuals in the special strains used by Swingle in his breed- 

 ing work, no data are given, so that it can not be affirmed that 

 inbred progeny from them would have been duplicates as far as 

 hereditary characters are concerned. Citrus plants naturally 

 cross fertilize, and from this cause alone no dependence can be 

 placed on their ability to produce progeny, which are exact dupli- 

 cates of themselves when inbred ; in fact, the inference is that 

 they would not. Hence, as far as intraspecific constancy of 

 hereditary characters is concerned, Swingle's statement can not 

 be accepted until more exact information is produced. 



Swingle says no interspecific gradations occur between these 

 various species, especially C. trifoliata and C. aurantium. Grant- 



