36 BULLETIN 564:, U. S. DEPARTMENT OF AGRICULTURE. 



range in the seasonal averages of the five plats was only 4.5 per cent 

 and the seasonal average infestation of the three picked plats was 

 47.6 per cent while that of the two checks was 47.9 per cent. 



EFFECT ON PLANTS. 



The same effect of the picking operation on the plants was observed 

 in this test as in all other bag-and-hoop experiments. It was 

 observed that the shakings were reducing the size of the plants and 

 were causing the typical bushy growth. One thousand plants were 

 measured in each of the plats to determine the average height on 

 July 19, 200 plants being examined at five different points in each plat. 

 The results secured are shown in Table 31. 



Table 31. — Average height of plants on July 11, Eureka plantation, Tallulah, La., 



1916, Test No. 1. 



Plat Xo. 



Treat- 

 ment. 



Average 

 height. 



1 



Cheek 

 Shaken . . . 

 ...do 



Inches. 

 42.7 



2 



35.4 



3 : 



37.9 



4 



...do 



37.5 





Check 



40.6 







From this it is seen that the two checks averaged 40.6 and 42.7 

 inches in height, while the next highest plat was 3, which averaged 

 37.9 inches; plat 4 was practically the same height, averaging 37.5 

 inches, while plat 2 showed the greatest effect of all, averaging 35.4 

 inches. These differences had been more pronounced earlier in the 

 season, but, following the cessation of shaking, the picked plats had 

 recovered a portion of the lost height by a rapid terminal growth. 



The difference in height between plats 1 and 2 is illustrated photo- 

 graphically in figure 2 of plate 2, which shows the dividing line between 

 these two plats. 



From these figures showing the effect of the shaking of the plants it 

 is seen that plat 2 was the most seriously injured of the series, while 

 plats 3 and 4 were affected practically the same. This would seem 

 to indicate that it is the duration of the pickings rather than the 

 number which determined the effect on the plants. For example, 

 plats 2 and 3 received the same number of shakings, but the interval 

 was twice as long in plat 2 as in plat 3, so they extended much later 

 into the season and the result was that in the fall plat 2 showed a 

 much greater injury. Plat 3 received two more pickings than plat 4 

 but the time intervals differed so that the pickings extended over 

 about the same period in the two plats and the resultant effect on 

 the plants was much the same. 



