STERILITY IN RELATION TO HORTICULTURE 1 
M. J. Dorsey 
The sterility problem in horticulture will be discussed from the stand¬ 
point of those factors which limit the crop. Since most of the principles 
involved are encountered in pomology, the discussion will be limited to this 
field. Recent investigations have dealt with many of the causes of what 
the fruit-grower designates as a crop failure. In the broader sense the 
sterility problem has its setting in the factors which influence the initiation 
and formation of fruit buds as well as in those which bear upon the set of 
fruit. It will be evident that, in all of those fruits in which the edible 
portion includes a ripened ovary, bloom must precede the production of 
fruit. Let us for the moment, then, keep in mind the point of view of the 
horticulturist in analyzing the causes which bear upon the set of fruit. 
Before taking up the discussion of the individual fruits, emphasis will be 
placed for the sake of clearness upon some general considerations. 
First: The variety is the unit in horticulture. Varieties may be dis¬ 
cussed in the classroom and in the laboratory in terms of species, but in 
the orchard and on the market the variety is the unit. The present ten¬ 
dency, however, in breeding horticultural plants to make so many inter¬ 
specific crosses will tend to bring the characteristics of the species to the 
foreground, and at the same time, especially in “wide crosses,” to increase 
the difficulties in the setting of fruit because the hybrid condition may have 
an important bearing upon the formation of pollen and embryo sac. 
Second: The ratio between the number of flowers produced and the 
number of fruit to set, or to mature, varies in the different fruits. In the 
apple or plum, for instance, a set of five to ten percent of a full bloom is 
sufficient for a crop. It would be physically impossible for the tree to 
mature a fruit for each flower in the apple, pear, plum, or peach. On the 
other hand it is possible for all the pistils in the grape, raspberry, blackberry, 
strawberry, or currant to set and mature. Likewise, the number of seeds 
necessary for fruit development varies. Some fruits are seedless, like the 
banana and the seedless grape; others, like the peach or plum, require a 
single seed for development; while in the apple and pear the number of 
seeds present in ripe fruit differs with the variety and also from season to 
season. In the strawberry or raspberry, where the development of the 
edible fruit reaches perfection only when a high percentage of the achenes 
or drupelets set, many more ovules fail to develop in marketable fruit than 
1 Read in the symposium on “Sterility in Plants,” at the joint meeting of Section G 
of the American Association for the Advancement of Science, the Botanical Society of 
America, and the American Phytopathological Society, at Cambridge, December 27, 1922. 
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