THE EFFECTS OF SELECTION 



THE well known maize breedin*^ 

 experiments at the Illinois Agri- 

 cultural Experiment Station 

 represent, it is said, the longest 

 continued breeding experiment now in 

 existence, with that cereal, which ranks 

 second only to rice in its importance as a 

 food crop of the world. L. H. Smith 

 describes some of the results as follows : 



"Starting in 1896 with an ordinary 

 variety of corn that contained at that 

 time 10.9% protein, there has been 

 produced after seventeen years a strain 

 which now contains 14.83%, while on 

 the other hand by selection for low 

 protein there has been produced another 

 strain which contained in last year's 

 crop 7.71% protein. In other words, by 

 the method of continuous selection of 

 seed there have been gradually developed 

 out of the original variety two quite 

 different kinds of corn, one of which is 

 practically twice as rich in protein as the 

 other. 



"Again, starting with this same 

 variety of corn which contained origin- 

 ally 4.7% oil, it has been possible to 

 produce a strain that contained in the 

 crop of last year an oil content of 8. 15% ; 

 whereas, selecting in the opposite direc- 

 tion has resulted in a strain that ana- 

 lyzed last year 1.9% oil. Or, expressed 

 in other words, by this method of 

 breeding, it has been possible to start 

 with a single variety of corn, and produce 

 two different sorts, the one of which is 

 now more than four times as rich in 

 oil as the other. 



"In 1903, a variety of corn was 

 taken for selection to modify the height 

 at which the ear is borne, and selection 

 for high ears and for low ears has 

 continued since that time. Because of 

 two unfavorable and rather abnormal 

 seasons during the past two years, the 

 results have not been so striking as those 

 obtained in 1912, when the ears of the 

 high-ear strain were borne at an 

 average height of 78 inches from the 

 ground, as compared with 25 inches in 

 the corresponding low-ear plot. Thus 

 there was an average difference amount- 



ing to over 43^ feet, a' most graphic 

 demonstration of the power of selection 

 in corn to influence certain character- 

 istics with respect to habit of growth. 



"Another line of selection affecting 

 habit of growth was begun in 1904 in 

 which the endeavor has been to modify 

 the angle at which the ear hangs on the 

 stalk. In one strain the selection has 

 always been for ears standing erect 

 while in a corresponding strain the seed 

 has been chosen from ears that hang 

 downward. The comparison is made 

 each year by measuring the angle at 

 which the ear declines from the per- 

 pendicular. Last season's results gave 

 an average of 66 degrees for the erect 

 ears as compared with 124 degrees for 

 the declining. This particular habit is 

 one that is easily affected by environ- 

 mental disturbances and this last year's 

 results are not so striking as that 

 obtained two years ago when the average 

 difference in angle between the two 

 strains amounted to 73 degrees. 



"Still another line belonging to this 

 same general category of selection to 

 modify physical characteristics of the 

 corn plant is that which was started 

 ten years ago to develop from an ordi- 

 nary single-eared variety a strain which 

 should bear two ears to the stalk. In 

 the season the first selection was made, 

 the proportion of two-eared stalks was 

 only 23^%. This proportion has been 

 very materially increased, varying greatly 

 in different years with the environ- 

 mental influences, but on the whole 

 showing a marked response to the 

 selection so that last season the propor- 

 tion of two-eared stalks was the highest 

 that has yet been attained, namely 73%. 



"In addition to the experiments 

 above described to modify through the 

 method of continuous selection these 

 physical and chemical characteristics 

 of corn, there is being conducted a 

 comprehensive fundamental study of 

 heredity in maize with reference to the 

 unit characters and their modes of 

 transmission. This investigation is 

 being conducted mainly by the method 



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