38 BREEDING CROP PLANTS 



mas protrude from the glumes and take a pendent position before 

 anther dehiscence takes place. 



Cotton. Probably cotton crosses to a greater extent than any 

 of the other plants, except sorghums, listed as belonging to the 

 naturally self-fertilized group. Because of the difference in ob- 

 servations by investigators it would seem that varietal differences 

 are one probable cause for the discrepancies. 



Leake (1911) observed 5 per cent, natural crossing in India. 

 Figures given by Webber (1905) and Balls (1912) range from 5 

 to 13 per cent. 



Grain Sorghums. Ball (1910) states: 



"All sorghums are adapted to open or wind pollination and most of 

 them are probably adapted to self-fertilization. In adjacent rows of 

 different varieties flowering on approximately the same date, as high as 

 50 per cent, of the seed produced by the leeward row was found to be 

 cross-pollinated. It is probable that in a fairly uniform field of any 

 given variety a similar percentage of natural crossing takes place." 



Graham (1916), in India, made a careful study of the amount 

 of cross-fertilization in the Juar plant (Andropogon sorghumBrot.). 

 Crossing was more frequent in the looser types of inflorescence 

 than in the compact types. Single plant cultures were used for 

 the study, which extended over a period of seven years. The 

 percentage of crossing obtained by counting a given number of 

 plants and noting those which were untrue to type gave 97 plants 

 out of 1,577 (6 per cent.) in the loose headed type and only two 

 plants out of 292 (0.6 per cent.) in the compact type of panicle. 

 Preliminary studies were made by Karper and Conner (1919) 

 of the amount of cross-pollination in plants of white milo which 

 were found growing in a plot of yellow milo. The yellow and 

 white varieties flowered simultaneously. Forty-one heads of 

 white milo, which had been surrounded by yellow milo, were 

 planted the following year. An average of 6 per cent, of natural 

 crossing in plants so surrounded was noted. 



Peas and Beans. Piper (1912) finds that natural crossing in 

 the cowpea occurs but rarely in most localities. At Arlington 

 Farm, in the experimental plots, instances of natural crossing 

 have been observed. In some instances natural crossing occurs 

 more frequently. Thus an Indiana farmer, who originally grew 

 only eight varieties, found after several years that he had over 

 40 types. The new types, Piper concluded, were the result of 



