Feb. 16, 1914 
Citropsis, an African Genus Allied to Citrus 
435 
GRAFTING OF CITROPSIS 
Experiments conducted under the directions of the authors in the 
greenhouses of the Department of Agriculture at Washington, D. C., show 
that Citropsis Schweinfurthii can be grafted readily and that it will grow 
rapidly and vigorously on sweet orange, sour orange, grapefruit, and 
lemon stocks. It can also be grafted on the tabog ( Chaetospermum gluti- 
nosa) and the wood-apple (Feronia elephantum) , two stocks on which 
species of Citrus graft readily. However, it does not grow as vigorously 
on these stocks as on Citrus. The very rapid growth of Citropsis when 
grafted on Citrus (see PI. XUX) is an added and striking proof of the close 
affinity of these two genera. Additional experiments in budding and 
grafting on other genera related to Citrus are now under way. 
In view of the considerable botanical differences between Citrus and 
Citropsis, it is probable that the latter will show immunity to diseases and 
adaptations to soil and climatic conditions not. possessed by the stocks 
upon which citrous fruits are commonly grafted. Experiments conducted 
by the authors have already indicated that Citropsis Schweinfurthii is well 
adapted to poor, sandy soils (“high pine lands” ) in Florida. Every new 
stock well adapted to Citrus gives the grower and the pathologist a new 
tool in the work of perfecting the culture of citrous fruits and in prevent¬ 
ing the ravages of diseases by using stocks which are immune. The 
scarcity of material of the African cherry oranges has hitherto prevented 
any extensive experiments in the use of this new stock, but grapefruit 
and oranges have both been budded successfully on Citropsis stocks in 
the greenhouse at Washington and out of doors in Florida. 
HYBRIDIZATION OF CITROPSIS 
The fact that there are a number of closely allied yet distinct species 
of Citropsis native to the forests of tropical Africa is an advantage to the 
plant breeder in furnishing material for the improvement of the African 
cherry oranges by hybridization. Whether the waxy-fruited species will 
yield edible hybrids when crossed with the juicy-fruited species can only 
be told by experiment. 
So far, the scarcity of flowers of the African cherry oranges has pre¬ 
vented any decisive test as to whether they can be crossed with species 
of Citrus or not. This much can be said, that flowers of the common 
lime, Citrus aurantifolia (Christm.) Swing., pollinated with Citropsis 
Schweinfurthii set fruit and produced seed. Only a few seed were se¬ 
cured and none of them gave rise to a hybrid, but this is not uncommon 
in Citrus. The fact that the pollen of Citropsis was able to cause the 
development of seeds is a very hopeful sign that hybrids will be secured 
from pollinations in the course of the breeding experiments now being 
carried on by using the pollen of Citropsis on as many species of Citrus 
as possible. 
