136 



Journal of Agricultural Research 



Vol. VI, No. 3 



ULTIMATE EFFECT OF INJURY UPON THE PLANTS 



The preceding pages have shown the different insects contributing to 

 the mutilation of cotton seedlings, but it is the ultimate effect upon the 

 cotton production of the plants which determines the economic impor- 

 tance of the injury. This is a point upon which it is difficult to secure 

 accurate data, but a certain amount of information has been gathered by 

 the writers. 



A number of plants are evidently killed outright by the feeding of the 

 insects; but this number appears to be so small, even in fields very heavily 

 infested, that it is of no practical importance. 



The leaf feeding is also of very doubtful importance. In severe cases 

 it retards the growth of the plants somewhat and occasionally dwarfs 

 them permanently, but usually they recover very rapidly, and there is no 

 visible effect other than the slight retardation. 



Apparently it is the injury to the terminal buds which produces the 

 most important economic effect. When this bud is injured or destroyed, 

 the development of the plant is greatly changed. Instead of having a 

 single main stem extending to the top of the plant, two or more large 

 branches develop just below the injured bud and serve as stalks to pro- 

 duce the fruiting branches. Usually several very abnormal clusters of 

 leaves form around the stalk near the injury. In Plate XVI, figure 2, 

 the result of similar injury is shown in comparison with a normal plant. 

 These two plants were collected in the garden at the laboratory and 

 were stripped of their leaves before being photographed. Plant B shows 

 a normally developed stalk and its branches, while plant A shows the 

 deformity caused by the destruction of the terminal bud. 



About the middle of June a number of examinations were made in the 

 fields near Tallulah in order to determine the abundance of these deformed 

 plants. The results of these examinations are given in Table V. 



Table V. — Records of field examinations for deformed cotton plants at Tallulah, La. 



June 8. 

 9 

 9- 

 10. 

 II. 

 II 

 16. 

 17- 



Total 



Weighted average. 



Number of 



plants 

 examined. 



4, 000 

 100 

 100 



1, 000 

 100 

 500 

 400 

 600 



6,800 



Number of 



plants 

 deformed. 



3 

 7 



87 

 4 



63 



42 



553 



Percentage 

 deformed. 



7.8 



3-0 

 7.0 



8.7 

 4.0 

 12. 6 

 8.2 

 7.0 



Location. 



Plantation. 

 Hotbed.i 



Laboratory garden.^ 

 Plantation. 



Do. 



Do. 



Do. 



Do. 



' Just prior to this examination the plants in the garden and hotbed had been hand thinned; and as the 

 poorest plants were removed, the percentage of deformed plants was evidently greatly lowered. 



