62 
SEVENTH ANNUAL MEETING OF THE 
Results in Crossing- Navel Oranges. 
Bv Pro f essor H. J. Webber, of the Sub Tropical Laboratory, of the 
U. S. Department of Agriculture, Eustis, Fla. 
In our work on the orange and its diseases at the Sub- 
Tropical Laboratory our attention was early drawn to the un¬ 
fruitfulness of the navel oranges in Florida. The various 
conflicting opinions of orange growers relating to the absence 
of fuliy developed pollen in the navel flowers, and contrasted 
with this the apparently current effect of navel pollen in acci¬ 
dental crosses, lead to experiments along this line. The ex¬ 
periments are by no means concluded, but have already 
yielded, at least very interesting suggestions. 
It has been suggested by some that the unfruitfulness of 
navel orange trees in Florida was to be attributed to the ab¬ 
sence of fully developed pollen in the navel flowers. In Cali¬ 
fornia, however, it is asserted that the navel trees bear an 
abundance of fully developed pollen, and thus their fruit¬ 
fulness. 
Again it is commonly claimed that the navel oranges pro¬ 
duced occasionally on common sweet orange trees, and Man¬ 
darin trees are to be accounted to accidental crosses with 
pollen from navel orange trees. 
A careful examination was made with a good compound 
microscope, of many anthers of navel flowers, from both Cali¬ 
fornia and Florida. This has shown that perfect, fully de¬ 
veloped pollen is seldom if ever produced in navel flowers. 
In only two cases was any pollen found, and in these instances 
one could by no means be sure that it had attained full nor¬ 
mal development. It is thus probable that the isolated cases 
of navel orange fruits on the common sweet orange tree will 
have to be explained in some other manner. I will not, how¬ 
ever, speak of this point at present. 
Microscopic studies of the development of the flower and 
fruit of the orange, have shown that navel oranges as well as 
the common sweet orange, grape fruit, sour orange, etc., form 
in the embryo sac more than one embryo. They are poly- 
embryonic. Only one of these embryos is fecundated and 
developed. Frequently some of the others develop, but 
without fecundation. It was thus suggested to me that prob¬ 
ably the development of these unfecundated embryos might 
