Hayes and Garber - Cucurbit Breeding

68 BREEDING CROP PLANTS
Two men may well work together in pollination. One unties
the ear bag and the other shakes the dead anthers from the
tassel bag and pours the pollen over the silk. Care is needed
in performing this operation to prevent cross- or uncontrolled
pollination. In producing biotypes by self-fertilization the
occasional cross may easily be rogued out as the crossed plant
will plainly be seen the following year because of its vigor and
other characters. Some workers prefer transparent paper bags
which allow the development of the silks to be noted without
removing the bag from the ear, and thus save unnecessary work.
Hard showers or long continued rains seriously interfere with
the artificial pollination of corn, as the tassel bag becomes wet
and makes the handling of the pollen difficult. A desirable
method is to remove the tassel bags after each rain and put on
new ones. As a number of days elapse from the time the first
pollen of the tassel matures until all is mature, the method
of replacing tassel bags gives good results.
Self-pollination of squash has been carried out at the
Minnesota Station. A little practice helps in determining when
a flower is about ready to open. The petals of both staminate
and pistillate flowers are prevented from opening by placing a
small rubber band around each one. On removing the band the
following day the flower quickly opens if it is ready for pollination.
The petals are then removed from the staminate flower
and the anthers rubbed over the pistil. The artificially pollinated
flower is protected from cross-pollination by placing a
rubber band around the petals. After a few days the petals of
the crossed flower abciss and at this time the stigma has turned
brown and is no longer receptive. This method was worked
out by John Bushnell, a graduate student in horticultural plant
breeding. From a total of 600 pollinations made under field
conditions in the summer of 1919, approximately 150 set fruit.
A thorough knowledge of flower struc-
Technic of Crossing.
ture of the species or variety to be worked with is essential before
crossing is undertaken. It is important to know which flowers
are the most vigorous and which set fruit the most freely.
Many
varieties of wheat, for example, produce several seeds per spikelet.
The outer florets of the spikelets in the central part of the
rachis are more vigorous and usually produce larger seed. In
some Solanacece (for example, the petunia) the later flowers
form larger, healthier seed than those which first open (East,