GENETICS: D. F. JONES 
247 
generation of continuous self-fertilization, are remarkably uniform and con- 
stant. Very little change in average ear row number or reduction in varia- 
bility of row number has taken place after the eighth generation in two inbred 
lines derived originally from the same plant in the second generation of in- 
breeding as shown in figure 1. These results are in agreement with the 
theoretical attainment of nearly complete homozygosis automatically in about 
the eighth generation of self-fertilization. Although the inbred strains are 
now only about one half as productive as the original variety, the plants, 
judging from their behavior in the past three years, are capable of being 
maintained unchanged indefinitely by self-fertilization. 
J , , 1 -r — r- 1 1 1 I ' 
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Generations Inbred 
FIG. 1. 
In contrast to the uniformity of all the plants within one inbred line is 
the difference between the several lines. With regard to ear characters two 
of them have flat cobs and two have round. One has uncolored cobs while 
the others have colored. They all differ in the shape and size of ears and 
seeds and in the arrangement of the seeds on the ears. Equally noticeable 
differences characterize the tassels, stalks and leaves. 
One of the most pronounced effects of inbreeding in maize is the appear- 
ance of sterility in the form of pollen and ovule abortion. An extreme reduc- 
tion in the amount of pollen produced is shown frequently in plants long 
inbred. Not all strains show this, however, as some have well developed 
anthers and produce abundant pollen. In nearly every case, however, those 
inbred strains which have the best developed staminate inflorescences have 
poorly developed pistillate inflorescences and those strains which have the 
