JOURNAL OF ACRK1TIAL RESEARCH 
Voiy. XXIII Washington, D. C., January 27, 1923 No. 4 
TWO IMPORTANT NEW TYPES OF CITROUS HYBRIDS 
FOR THE HOME GARDEN—CITRANGEQUATS AND 
LIMEQUATS 1 
By Walter T. Swingle, Physiologist in Charge , and T. Ralph Robinson, Crop 
Physiologist , Office of Crop Physiology and Breeding Investigations , Bureau of Plant 
Industry , United States Department of Agriculture 
The breeding of cold-resistant citrous fruits suitable for culture in 
the southern part of the cotton belt has been in progress for many years. 
The citrange, a cross of the hardy Chinese trifoliate orange, Poncirus 
trifoliata (L.) Raf. and the common sweet orange, Citrus sinensis , Osb. 
was the first of the hardy hybrids secured. The citrange was first 
reported on by the senior author and Dr. H. J. Webber 2 in the Yearbook 
of the Department of Agriculture for 1904, where the Rusk and Willits 
citranges, two that appear below as parents of new hybrids, were de¬ 
scribed and illustrated. It soon became evident that although the cit¬ 
range is much like the trifoliate orange in its resistance to extreme cold 
when it is in a dormant condition, it is easily forced into a new growth 
in spring and sometimes is severely injured by untimely cold snaps. 
In consequence of this imperfect resistance of the citrange to spring 
and early autumn frosts, about 15 years ago the effort was first made to 
create new types of hybrids which would partake in some measure of 
another type of hardiness possessed very strikingly by the kumquat 
oranges. The kumquat is one of the hardiest of the evergreen citrous 
fruit trees; besides having a fair degree of resistance to cold it has an 
extremely high degree of winter dormancy. Both of the species of 
kumquat commonly grown in this country, the round and the oval kum- 
quats, are able to pass unaffected through spells of hot weather which 
force other citrous into a tender and succulent growth that is liable to be 
injured by a slight frost. 
The first successful hybrids wherein the kumquat was used with the 
idea of securing increased dormancy were made by the senior author in 
the spring of 1909. Four principal types of these kumquat hybrids 
were made: First, those between Idle trifoliate orange and the kumquat. 
These proved extraordinarily hard to make, and most of them were very 
weak, many of them dying while still small seedlings. None of these 
have proved as yet to be of any considerable value. Second, hybrids 
were made in considerable number between the more promising citranges, 
especially the Rusk and Willits, already widely cultivated in the cotton 
belt, and the kumquats. The hybrids resulting from these crosses are 
known as citrangequats, and are described in the present paper. Third, 
the effort was made to hybridize the kumquat with the West India lime* 
1 Accepted for publication Oct. 28, 1921. 
1 Webber, Herbert J., and Swingle, Walter T. new citrus creations OP THE department op 
agriculture. In U. S. Dept. Agr. Yearbook, 1904, p. 227-235, fig. 13, pi. 11-14, 16. 1905. 
Journal of Agricultural Research, Vol. XXIII, No. 4 
Washington, D. C. Jan. 27, 1923 
acl Key No. G-270 
22330—23-1 
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