126 INBBEEDING AND OUTBKEEDING 



In 1916 and 1917 the inbred strains were grown in some- 

 what larger plots and the yields are fairly reliable. 



With these points in mind, an examination of the table 

 shows that from the beginning of the experiment to the 

 ninth generation there has been a tremendous drop in 

 productiveness, so that in that generation the strains were 

 approximately only one-third as productive as the variety 

 before inbreeding. From the ninth to the eleventh gen- 

 eration there has been no reduction in yield and prac- 

 tically no change in visible characters. Height of plant, 

 as far as the available figures show, followed the same 

 course. The reduction which has taken place occurred in 

 the first eight generations ; after that there has been no 

 appreciable change. 



All along the several Learning strains have shown 

 considerable differences in productiveness and in height. 

 Strain No. 1-6 has given the largest yields and the tallest 

 plants. It gave nearly 50 per cent, larger yields than the 

 poorest yielding strain in the eleventh year, and was about 

 30 per cent, higher than the shortest strain. 



One of the strains, No. 1-12, was lost in the sixth gen- 

 eration. Previous to this time it had been the poorest of 

 the five. It was partially sterile, never produced seed at 

 the tip of the ear and was perpetuated only with care. 

 Since the difficulty of carrying along any inbred strain is 

 great, owing to failure to pollinate at the correct time, to 

 attacks of fungus on the ears enclosed in paper bags, and 

 to poor germination in the cold, wet weather common in 

 New England at corn-planting time, the loss of this strain 

 might be easily accounted for without assuming continu- 

 ous deterioration. The strain probably could have been 

 retained if sufficient effort had been put forth; but in 



