STUDIES ON OAT BREEDING. 99 



tion type, and which differ in the direction towards which selec- 

 tion was made. Thus if one begins in a general mixed popula- 

 tion of beans to select for planting the largest beans, and by to 

 doing increases the average size of the beans in the crop, what 

 he really does is gradually to throw away all beans except those 

 which belong to strains having large beans as the type. Having 

 isolated from the population one of these component strains 

 which breeds true to a definite type no amount of further selec- 

 tion will modify that strain. 



The idea underlying these conclusions is that, in the continued 

 propagation of the offspring of any self- fertilized plant, every 

 individual will possess exactly the same hereditary constitution 

 as every other individual. Consequently except for the ^effect 

 of environmental conditions such a "pure line", as it is called, 

 should breed true and should show the same characters in every 

 generation. 



The same reasoning cannot, without some modification, be 

 applied to open fertilized plants, such as corn for example. Here 

 any individual kernel, in the majority of cases, has been fer- 

 tilized by pollen from some neighboring plant. This latter plant, 

 and consequently its pollen grains, may be carrying characters 

 very different from those of the mother plant. The offspring of 

 such a grain would split up, some showing characters similar to 

 the pollen parent and others like the mother plant. By continued 

 self-fertilization (hand pollination) of corn a condition ap- 

 proaching that of a pure line could be obtained. 



The majority of our cereals, such as oats, wheat, barley, etc., 

 are nearly always self-fertilized. Wilson 4 says that natural 

 crossing occurs only very rarely in oats. Rimpau found only 

 five spontaneous crosses in dealing with 19 different varieties 

 during a period of six years. In our own experience we have 

 never observed a single natural cross although in our oat gar- 

 dens different varieties including black, white and yellow oats, 

 open and side heads, have been grown in adjacent rows. These 

 rows are only one foot apart and at the time of blooming the 

 heads of one row interlock with those of the next. The reason 



4 Wilson, J. H. The Hybridization of Cereals. Journ. Agric. Sc, Vol. 

 2. pp. 68-88, 1907. 



B Rimpau, v. Kreuzungsproduktion Landw. Kulturpflanzen. Landw. 

 Jahr. 1891. 



