412 
eties of plums are self-sterile; Waite (U. 
S. Division of Vegetable Pathology, Bull- 
etin 5) shows results of many experi- 
ments carried on with the pear to show 
the affinity of certain varieties for the 
pollen of certain other varieties. Some of 
the most interesting discoveries made by 
Waite are, that the descriptions given by 
Warder, Thomas and Downing were true 
only for the fruits resulting from cross- 
fertilization; that the fruits from cross- 
fertilization were much larger and that 
the flavor was much better in the crossed 
varieties than the fruits resulting from 
self-fertilization. 
Everyone has noticed that isolated fruit 
trees failed to bear fruit though they 
blossomed full each year. The Wild 
Goose plum is a very good illustration of 
this self-sterility in fruit trees, familiar to 
everyone who has planted this variety in 
isolated positions. 
This self-sterility, as it is called, is the 
inability of the pollen of a plant to fer- 
tilize its own ovules or those of other 
plants of the same horticultural variety 
and is indicated in fruit trees by the con- 
tinued dropping of the fruiting organs be- 
fore the fruits have become well formed, 
although fruits often drop from other 
causes, as frost, general debility of the 
tree, etc. 
No one can say why a variety should 
refuse its own pollen and accept that of 
another variety. Accepting Darwin’s law 
that “Perpetual self-fertilization is injuri- 
ous and results in inferior and less fertile 
offspring,” we would admit, that, in the 
countless ages of the selection of the 
apple, inferior offspring and, perhaps, the 
entire loss of fertility has been avoided 
by self-sterility. In the apple, self-fertil- 
ization has been guarded against in differ- 
ent ways, aS will be seen in the descrip- 
tions and experiments which follow. 
Definition of Terms Used 
Self-sterility: Inability of pollen to 
fertilize ovules of same _ horticultural 
variety. 
Self-fertile: A plant is said to be selt- 
fertile when the pistil will accept pollen 
from a plant of the same horticultural 
variety. 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
Cross: Union of pollen cell and ovule 
of two distinct horticultural varieties. Ip 
no case is it meant the transter of pollen 
from one flower to another on the Same 
tree or from one flower of a variety to the 
pistil of another individual tree of the 
same horticultural variety. 
Pollination: Act of transferring of 
pollen to the pistil. 
Fecundation: Union of pollen cell and 
the ovule. 
Fertilization: A general term to in- 
clude both the preceding terms. 
The flower of the apple is regular ang 
perfect in all of its parts; petals anq 
sepals five, petals varying in color from 
Fig. 1. No. 1. Cullen Stamens Before Dehise- 
ing. No. 2. Cullen Outer Row of Stamens 
Dehisced. 
a pure white to a faint rose; stamens 20 
or less, filaments of two lengths, one set 
of anthers ripening later than the other 
(see figure 1), anther two-celled dehiscing 
along the outer margin, the two cells not 
always dehiscing at the same time but 
the dehiscance of both taking place within 
a very short period; pistils ripening be- 
fore the stamens, stigma extremely papil- 
lose and in a condition to catch and retain 
pollen before it is receptive, though it is 
in a receptive condition as soon as the 
flower opens; stigma secreting a sticky 
fluid which also aids in holding pollen 
