RETARDING INFLUENCE OF CROWDING 



127 



and 150 hens each. The pens with the smaller flocks provided 4.8 sq. 

 ft. of floor space per hen. In the largest flock this was reduced to 

 3.2 sq. ft. per individual. The number of pens is shown in Table II. 



In all there were 700 pullets placed in the 50-bird pens, 500 in the 

 IOC-bird pens, and 750 in the 1 50-bird pens. Conditions varied some- 

 what from year to year, so that Pearl and Surface warn that "wher- 

 ever comparisons between years are instituted, great caution must 

 be exercised in drawing conclusions." 



Due care was taken to select the members of the different pens 

 with hereditary constitutions equally disposed to egg-laying, so far 

 as this factor could be regulated. All were from the same breed, and 



TABLE II 



individuals were distributed among the different pens so that the 

 percentage from ancestors of different productivity were the same 

 throughout. The experiment with which we are concerned ran three 

 seasons. Results are graphically given in Figure 5, which shows the 

 mean annual egg production per hen. An inspection of this figure 

 shows that each year there is a trend toward reduced egg production 

 in the pens with the greatest number of birds. During two of the 

 three years the decrease in rate of laying is practically the same 

 between the 50- and the loo-chicken pen as it is between the 100 and 

 J50. The results obtained the first season, 1904-5, are different and 

 affect the mean differences, as is seen from the fact that the pens 

 with 50 birds produced on the average 129.69 eggs per season; 

 those with 100 produced 123.21, while those with 150 gave in. 68; 

 The mean difference between the pens with 50 birds and those with 

 150 amounted to 18.01 eggs per year. 



The difference between the loo-bird pens and the 1 50-bird pens, 

 where there were two factors acting — increase of numbers and de- 

 crease of floor space — is approximately twice as great during these 



