X = 



6 MAINE AGRICULTURAL EXPERIMENT STATION. I915. 



varieties of oats have been grown only one foot apart. At the 

 time of blooming the heads of one row interlock with those of 

 the adjacent rows. Although black, yellow and white oats, 

 open and side heads have been grown next to each other, we 

 have never observed a single natural cross. In no case were all 

 the grains of any one row planted individually the next year, but 

 in many cases a large per cent, of these have been grown. It 

 seems certain that under our conditions, at least, natural crossing 

 is extremely rare in oats. 



If this is true it can be shown that practically every oat plant 

 will be homozygous for all of its characters. Thus Jennings'^ 

 has shown that starting with the heterozygotic condition the pro- 

 portional number of pure homozygotes produced by continued 

 self-fertilization is given by 



where X = the proportional number of pure homozygotes, 

 n = the number of successive self-fertilizations and m = the 

 number of pairs of characters. From this we find that if there 

 are lo pairs of characters and 10 self-fertilizations, X = 

 0.97057 or less than three heterozygotes in 100. If there are 

 20 pairs of characters and 20 self-fertilizations X = 0.99999S 

 or only two heterozygotes in a million individuals. 



Since it is extremely probable that the ancestors of any given 

 oat plant have been self-fertilized for many generations, it 

 may be assumed that every oat plant is homozygous for all 

 of its characters unless, indeed, the number of separately in- 

 herited characters is very great ('ieveral thousand)." In this 

 respect the oat plant furnishes excellent material for the study 

 of selection within pure lines. 



In 1910 a large number of individual plants were selected 

 from the variety test plots of that year. Each of these plants 

 was harvested and threshed separately. In 191 1 the seed from 

 each plant was grown in a single row in the oat garden. Each 

 row contained 25 plants. The seed was planted by hand. The 



'"'Jennings, H. S. The Production of Pure Homozyg-otic Organisms 

 from Heterozygotes by Self-fertilization. Amer. Nat., Vol. XL VI, pp. 

 487-491, 19 1 2. 



"With 1000 characters and 20 self-fertilizations there would be less 

 than 5 heterozygotes in 1000 individuals. 



