Nov., 1923] 
DORSEY — STERILITY AND HORTICULTURE 
475 
is generally supposed. It will be seen, therefore, that the opportunity for 
development of both pistil and seed has an important bearing upon the 
subject at hand. 
Lastly, fruit-setting is complicated by the fact that fruit-bud initiation 
and development accompany fruit-production in some of the fruits, making 
it necessary to maintain conditions favorable to both. Where fruit buds 
are formed before dormancy, winter killing, especially in the peach, plum, 
and cherry, may exceed all other factors in reducing the crop. 
When planted alone and pollinated with its own pollen, a variety is self- 
fertile or self-sterile. Likewise, in mixed plantings the relationship with 
other varieties is cross-fertile or cross-sterile. The self- or cross-relationship 
is definite in some combinations and in others is intermediate or variable. 
With these relationships in mind, let us note briefly the extent of sterility 
in each of the different fruits as indicated by the more recent investigations. 
Status of Sterility in the Different Fruits. In the apple the status of self- 
and intervarietal-sterility or fertility is not so well defined as in some of the 
other fruits. The self-sterile, self-fertile, cross-sterile, and cross-fertile 
conditions occur in all different degrees. Other factors limiting production 
are alternate bearing, or the so-called “off year,” the coming into bearing 
late of some varieties, as Northern Spy, and the light bearing, even of older 
trees, which so often happens with Black Twig. The flower of the apple is 
perfect, and in most varieties the pollen is abundant. Bagging experi¬ 
ments indicate that about two thirds of the varieties are self-sterile (Lewis 
and Vincent, 1909; Gowen, 1920; Dorsey, 1921). Cross-sterility has been 
reported in only a few combinations and does not appear to be as important 
as self-sterility. When there is a full bloom a ten percent set is sufficient 
for a crop. Cultural conditions have an important bearing upon the 
formation of fruit buds as well as upon fruitfulness. In the apple, then, 
self- and cross-sterility, alternate bearing, the light setting of fruit buds, and 
coming into bearing late are the important considerations. Any one of 
these, or two or more, acting together may be limiting factors in production. 
The pear has many characteristics in common with the apple. The 
flower is perfect, and normal pollen and pistils are produced in sufficient 
quantities. A study of 36 of the principal varieties showed that out of this 
number 22 were self-sterile (Waite, 1895). As in the apple, varying degrees 
of self- and cross-sterility exist. The size of fruit is correlated with the 
number of seeds. Cross-pollination is essential to fruitfulness in a number 
of the most important varieties. Self-sterility was first demonstrated in 
the pear by Swayne in 1828. 
In the peach, sterility has not been found to be an important commercial 
problem. Investigations at a number of stations indicate that most 
varieties are self-fertile and cross-fertile, or at least sufficiently so to give 
an adequate set for a crop (Whitten, 1913; Fletcher 1909-10; and others). 
On the other hand, in California all varieties of the almond tested were 
