Hayes and Garber - Cucurbit Breeding

FRUIT BREEDING 271
Knight (1917) has made a study of self-sterility in the apple and
the conclusions reached show the manifold causes which must be
considered in a study of the problem. For this reason the
conclusions are here given verbatim.
"1. Self -sterility in Rome Beauty is not due to sterility of the pollen
as has been shown to be the case in certain varieties of grapes.
"2. Sensitiveness of pollen to over-abundant moisture supply is not
involved here as a factor, as ha-s been shown by Jost for the pollen of
N. Martin for the pollen of
many grasses, barley especially; and by J.
red clover. The pollen of Rome Beauty and many other varieties
germinated in distilled water.
"3. Rome Beauty stigmatic fluid extracts offer no inhibition to the
germination and growth of Rome Beauty pollen.
"4. Rome Beauty stigmas offer no particular mechanical obstruction
to the penetration of Rome Beauty pollen tubes.
"5. Self -sterility of Rome Beauty is not due to inability of its own
pollen tubes to grow deep enough to reach the egg. This has been suggested
as the cause of self-sterility in certain pear and apple varieties
by the work of Osterwalder.
"6. From present indications one important factor in self-sterility
of Rome Beauty is the relatively slow rate of growth pf Rome Beauty
tubes in Rome Beauty stylar tissue. Doubtless other factors will be
found upon further examination."
Inheritance of Some Characters. The mode of inheritance
of most fruit characters has as yet not been determined. There
are, however, numerous experiments under way for the purpose of
learning how individual characters behave in crosses. The lack
of information in this field is due to the heterozygous condition
of many fruit varieties and to the fact that with many fruit crops
so long a period elapses between the time of sowing the seed and
the production of fruit.
Apple. Inheritance in the apple is well illustrated by a
study made at the Geneva Station by Hedrick and Wellington
(1912). Crosses were made in 1898 and 1899 and 148 seedlings
were grown. In 1912, 106 of the seedlings had come into bearing.
These 106 seedlings resulted from 11 crosses. The first generation
naturally does not furnish very reliable data as a means of
deciding the mode of inheritance of individual characters.
Three types of skin color were studied, red, yellow, and intermediates.
The conclusion was reached that Ben Davis and
Jonathan were both pure for red color of skin, as crosses between