Hayes and Garber - Cucurbit Breeding

MODE OF REPRODUCTION IN RELATION TO BREEDING 37
visited by insects which may cause natural crossing. Fruwirth
(1909) states that crossing seldom takes place. Howard and
others (1910a) have observed natural crossing under Indian
conditions.
Some idea of the frequency of natural crosses may
be gained by a determination of the percentage of selected plants
which breed true. Results of this nature have been presented
by Howard and others (1919)
ṄUMBER
NUMBER
YEAR PLANTS BREEDING
SELECTED
TRUE
1916 340 334
1917 233 232
1918 232 232
Only 0.9 per cent, of the progeny rows showed segregation.
Rice. In rice the inflorescence is a terminal panicle of perfect
flowers. The one-flowered spikelet has a branched stigma and
six stamens. The lodicules are strongly developed. Fruwirth
(1909) observed the period of blooming in rice and found that
30 seconds elapsed from the time one flower began to open until
it was fully open. Dehiscence of the anthers occurred about
seven minutes later and the flower closed three hours afterwards.
In rice self-pollination is the usual method, although opportunities
for crossing occur. Hector (1913) thinks crosses may
occur at a distance of not more than 2 ft. by the agency of the
wind. In lower Bengal 4 per cent, of crossing was estimated.
Ikeno (1914) sowed alternate rows of blue- and white-seeded rice.
Xenia occurs, blue being dominant, if the white-seeded variety
is pollinated by the blue. Fifteen thousand kernels from 190
panicles were examined and no xenia was found. Thompstone
( 19 15) in , upper Burma, finds that pollination usually occurs before
the glumes open; however, hybrids were frequently observed in
fields of ordinary rice. Parnell and others (1918)
observed the
amount of natural crossing in pure green plants surrounded by
others which possessed seed with a purple tip. A total progeny
of nearly 15,000 plants grown from seed produced by the green
plants were observed, more than 2,000 plants being studied in
each of five different families. The percentage of crossing
varied from 0.1 per cent, in one variety to 2.9 per cent, in another.
Alkemine (1914) states that cross-pollination occurs if the
anthers, on account of unfavorable environmental conditions, do
not assume their natural position. This happens when the stig-