332 GENETICS IN RELATION TO AGRICULTURE 



protein corn. The next season 4 sound ears were analyzed from each 

 of the twenty-four rows. From these 96 ears the 24 again having the 

 highest per cent, of protein were selected for planting. The distribution 

 of these selected ears among the 24 original ears is shown in column two 

 of the tables. For example, it is seen that ear No. 124 produced 2 

 ears, Nos. 216 and 209, which were among the first 24 as regards protein 

 content. Ear No. 123 on the other hand failed to produce any ear (so 

 far as the ears analyzed showed) sufficiently rich in protein to be in- 

 cluded among the first twenty-four. Thus 8 of the original ears fail to 

 be represented in the second generation, while 8 other ears contributed 

 2 ears each for planting the following year. Exactly the same selection 

 was practised in the second year and the resulting selected ears are 

 shown in the third column of the tables. Of the 16 original ears rep- 

 resented in the second generation only one, No. 116, was dropped out 

 in the third generation but in the next generation there is a significant 

 dropping out of some of the original lines, so that in the fourth genera- 

 tion only 9 of the original 24 ears are represented by progeny. Five of 

 the original lines contribute 80 per cent, of this generation, while two 

 lines, 106 and 112, contribute nearly 60 per cent. Hence at the end of 

 the fourth generation it is clear that certain of the original lines have a 

 much greater tendency to produce ears with a high per cent, of protein. 

 By simply selecting on the basis of the protein content of the individual 

 ear for 4 years 70 per cent, of the original lines have been dropped. 



Thus the elimination of the original lines gradually proceeds until, 

 in the tenth and eleventh generations all of the high-protein corn is the 

 offspring of a single ear, viz., No. 121. It will be remembered that in the 

 tenth year the method of detasseling alternate rows and saving seed from 

 these only was put into effect. But this change in method could not 

 have induced the results we have noted because line No. 121 had demon- 

 strated its superiority over all the others as early as the seventh genera- 

 tion. This isolation of a single line was brought about therefore simply 

 by selecting each year those individual ears that showed the highest 

 per cent, of protein. Starting with a protein content of 10.92 per cent., 

 at the end of the third year (fourth generation, 1899) the protein content 

 was only 11.46 per cent, or a gain of 0.54 per cent. But the next year 

 (fifth generation) the protein content jumped to 12.32 or a gain of 0.86 

 per cent, in 1 year. Referring now to Table XLIX it is seen that it is in 

 1899 that a great reduction was made in the number of lines represented, 

 for in the fifth generation only six of the original twenty-four lines remain. 

 Furthermore it is just here that line No. 121 begins to show its superiority 

 since 5 of the 15 ears selected in 1900 or 33^ per cent, come from this 

 line. 



The course of events in the other three strains was similar but not 



