40 



BREEDING CROP PLANTS 



between the partly closed glumes until the bases protrude. 

 They then tip over and dehisce, spilling part of the pollen outside 

 the flower. Being lower than the stigma the pollen can not reach 

 the stigma of the same flower. There is some evidence (Ulrich, 

 1902) (Fruwirth, 1909) which indicates that the rye flower is 

 self-sterile, but that the spikelet is not necessarily so. Further 

 studies are needed to clear up this point. 



Ulrich (1902) found significant differences between varieties 

 and individuals of the same variety in the amount of self -sterility. 

 The following table shows some of his results, obtained from 

 artificial and natural pollination. Artificial pollination was 

 obtained by covering the head with double paper bags. 



TABLE II. SELF-STERILITY IN RYE 



Heribert Nilsson (1916) isolated lines in Petkuser rye differing 

 greatly in amount of self -sterility. Of 73 plant selections, 71 

 were practically self -sterile, one showed segregation, and one 

 proved to be highly self -fertile. The rye flower is probably 

 largely cross-pollinated and because of the heterozygous condi- 

 tion, strains differing in fertility make up any particular variety. 



Alfalfa. Piper and others (1914) working with alfalfa have 

 found about the same percentages of seed set when a flower 

 was self-pollinated as when it was crossed with pollen from 

 flowers on the same plant. When cross-pollination was prac- 

 ticed, approximately 50 per cent, more seed was obtained than 

 from self-fertilization. They also found that pollen of Medicago 

 falcata was as efficient in fertilizing M. saliva as pollen from other 

 saliva plants. 



Waldron (1919), in North Dakota, planted together in equal 

 numbers two species of Medicago, saliva and falcata. Seeds 

 from each of the species were planted the following year and the 

 number of hybrids noted. From M. falcata 42.7 per cent, of 



