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THE AMERICAN NATURALIST [Vol. XLVIII 



In 1908 an experiment was planned with the object of 

 developing a strain of wheat which would have a minimum 

 amount of culm exposed between the base of the spike and 

 the upper leaf sheath, or in other words, to produce a 

 short-necked variety of wheat. The ultimate purpose of 

 reducing the neck lengths was to reduce the area of the 

 stem exposed to the black stem rust. Since this rust 

 ordinarily docs little damage to that portion of the culm 

 enclosed in the leaf sheath, it was thought that a short- 

 necked wheat would be more likely to escape serious 

 damage from stem rust than a long-necked kind. For 

 this work individual plants were selected which had short 

 necks and the seed from these were planted in separate 

 centgeners. Kadi year at harvest time ten or more plants 

 which appeared to the observer to have the shortest necks 

 were selected from each centgener and measurements of 

 their neck lengths were made and recorded. One hundred 

 kernels were saved from these shortest necked plants 

 each season for subsequent centgeners, thus making a 

 continuous selection for short neck lengths. 



The data derived from the above experiments seems to 

 throw some light upon the much-discussed question as to 

 whether or not selection within a pure line can increase 

 yield or change type enough to make it a desirable prac- 

 tise from the practical breeder's standpoint. In both of 

 the experiments, we have the requirements for a pure 

 line satisfied. Wheat is a normally self-fertilized plant. 

 Each centgener was started from a single head in 1901 

 and these heads have bred true to type ever since. 



The long period of years over which this experiment 

 has extended makes the data particularly valuable. One 

 of the adverse criticisms to most pure line work is that 

 it has not extended over a long enough period of time. 

 Thirteen years are about as long as any practical breeder 

 would be apt to keep up selection on one pure line and 

 covers the longest period of continuous selection for a 

 self-fertilized plant yet reported. 



Another criticism to pure line investigations is that in 



