LEAF-CUT, A DISORDER OF COTTON SEEDLINGS. 33 
high it is easy to distinguish and remove the deformed individwals 
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. 
eee: 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 very abrupt. Plants that have had 
every leaf injured up to the sixth or eighth may then begin to put 
out entirely uninjured leaves. These abrupt changes may affect 
whole rows or fields of cotton, as if the later uninjured vegetation 
had grown out after a hailstorm. Whether the plants become im- 
mune to leaf-cut simply because larger stature carries the new 
erowth farther away from the overheated soil, or because a deeper 
root system affords a more regular supply of moisture, or because the 
weather 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 very similar to leaf-cut continued during the whole life of 
the plant. Some of these plants were hybrids and others were mu- 
tations, but all of them were abnormal in other ways, as well as in 
the irregular texture of the fohage. 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 leaves of the Durango cotton and other Upland varieties are often 
injured much more seriously than those of Egyptian cotton in adja- 
cent rows, but at the same time the Egyptian cotton may show a 
larger percentage of abortion of terminal and axillary buds. The 
immunity may le in the improvement 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, which may indicate the development 
of a different kind of immunity in this disorder. It is true that the 
plant lice usually disappear as the season advances, but even when 
the insects remain abundant the distortion becomes less as the plants 
grow larger. 
CONCLUSIONS. 
Leaf-cut 1s a disorder of cotton seedlings characterized by mutila- 
tion of the leaves and abortion of the terminal buds. Leaf-cut has 
