May 25 , 1914 
Eremocitrus 
97 
of accuracy the soil and climatic factors which limit the culture of the 
desert kumquat in the United States. 
THE UTILIZATION OF EREMOCITRUS IN BREEDING 
From the taxonomic study of Eremocitrus, it is clear that its nearest 
relationship is with the peculiar Australian species of Citrus (especially 
C. australis and C. australasica) , with which it shows close similarities 
in many characters of fundamental importance, such as the flower and 
fruit structure and the method of germination. 
This close relationship, deduced from the botanical characters, is 
confirmed by the fact that Eremocitrus glauca grows vigorously when 
grafted on Citrus australasica (PI. VIII, fig. 1) and that Citrus austra¬ 
lasica grafts readily on Eremocitrus glauca . It has been found that 
Citrus australasica hybridizes freely with at least two cultivated 
species of Citrus, 1 and it is not only almost certain that Eremocitrus 
glauca will cross with Citrus australasica and the other Australian species 
of Citrus, but also very probable that it will hybridize with the com¬ 
monly cultivated Asiatic species of Citrus. 
The desert kumquat, native to the semiarid Australian scrubs, able 
to withstand severe cold in winter as well as burning heat and extreme 
dryness both of the soil and air in summer, is the most promising 
species known for use in breeding new types of hardy citrous fruits. 
Every effort is being made to hasten its flowering, so that hybrids 
can be made, using it as one of the parents. The fact that the desert 
kumquat has edible fruits without any disagreeable acrid oil in the 
peel or in the juice makes it far more promising than the Chinese 
trifoliate orange, Poncirus trifoliata (L.) Raf. (= Citrus infoliata L.), for 
breeding hardy citrous fruits for table use. 
The discovery of this markedly drouth-resistant species in the Austra¬ 
lian scrubs opens the way to the breeding of a new class of citrous fruits, 
able to grow with much less water than is required by ordinary oranges, 
lemons, or grapefruits. 
GRAFTING AND BUDDING EREMOCITRUS 
The Australian desert kumquat can be readily grafted or budded on 
all of the commonly cultivated species of Citrus, such as the orange, 
grapefruit, lemon, etc., and also on the Australian finger lime (C. austra¬ 
lasica ). It grows very well on the tabog of the Philippine Islands 
(Chaetospermum glutinosa (Blanco) Swing.), and on the wood-apple of 
India ( Feronia elephantum Corr.). (See PI. VIII.) 
The various species of Citrus graft easily on Eremocitrus, which 
makes it possible to test this new hardy stock for types of soil to which 
1 Mr. George W. Oliver crossed Citrus australasica with C. miiis in 1909, and the writer crossed the same 
species with C. aurantifolia, the common lime, in 1913, in the greenhouses of the Department of Agriculture 
at Washington, D. C. Vigorous hybrids were secured from both of these crosses. 
