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). 



NUMBER 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 after.wards. 



In rice self-pollination is the usual method, although oppor- 

 tunities 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 

 (1915), 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- 



