LEAF-CUT, A DISORDER OF COTTON SEEDLINGS. 33 



high it is easy to distingiiiKli and remove the deformed individuals 

 and leave only the healthy and vigorous ones. Under the usual plan 

 of thinning the cotton early it is much more difficult to recognize and 

 remove the injured plants. 



SUSCEPTIBILITY AND IMMUNITY. 



Susceptibility to leaf-cut is usually limited to the seedlings and 

 young plants less than 10 inches high. Sometimes the change from 

 susceptibility to immunity is Aery abrupt. Plants that have had 

 every leaf injured up to the sixth or eighth may then begin to put 

 out entirely uninjured leaves. These abnipt changes may affect 

 Avhole roAvs or fields of cotton, as if the later uninjured vegetation 

 had groAvn out after a hailstorm. Whether the plants become im- 

 mune to leaf-cut simply because larger stature carries the new 

 groAvth farther away from the oA^erheated soil, or because a deeper 

 root system affords a more regular supply of moisture, or because the 

 Aveather conditions become more uniform as the season advances has 

 not been determined. All these factors may cooperate, or there may 

 be others as yet unsuspected. 



A few cases of abnormal individuals have been observed where 

 injuries Aery similar to leaf-cut continued during the Avhole life of 

 the plant. Some of these plants Avere hybrids and others Avere mu- 

 tations, but all of them Avere abnormal in other Avays, as Avell as in 

 the irregular texture of the foliage. It seems not unreasonable to 

 suppose that abnormal plants should remain more susceptible to any 

 external conditions that have adverse effects upon the activities of 

 the cells. 



Though all the different types and varieties of cotton seem to be 

 susceptible to leaf-cut injuries, certain differences have been noticed. 

 The leaA^es of the Durango cotton and other Upland varieties are often 

 injured much more seriously than those of Egyptian cotton in adja- 

 cent roAvs, but at the same time the Egy^ptian cotton may show a 

 larger percentage of abortion of terminal and axillary buds. The 

 immunity may lie in the improA^ement of conditions rather than in 

 an increased resistance on the part of the plant. With the plant-lice 

 injuries there is a gradual reduction of the amount of distortion that 

 the insects are able to produce, Avhich may indicate the deA^elopment 

 of a different kind of immunity in this disorder. It is true that the 

 plant lice usually disappear as the season advances, but even AAdien 

 the insects remain abundant the distortion becomes less as the plants 

 groAv larger. 



CONCLUSIONS. 



Leaf-cut is a disorder of cotton seedlings characterized by mutila- 

 tion of the leaves and abortion of the terminal buds. Leaf-cut has 



