LEAF-CUT, A DISORDER OF COTTON SEEDLINGS. 31 
lie in a somewhat radiating position between the principal veins. 
Healing of wounds and regeneration of lost parts show that the 
injuries are liable to occur at a very early stage in the development 
of the leaf. Sometimes an extensive new growth or regeneration 
takes place, resulting in a curious doubling or overlapping of lobes 
of injured leaves. The power of the injured tissues to heal is also 
responsible for adhesions between parts that lie folded together in 
the bud. These adhesions are usually responsible for failure of 
normal expansion of the blade. None of these secondary symptoms 
oecur with the leaf-curl induced by plant lice. 
CAUSES OF LEAF-CUT INJURIES. 
Leaf-cut is hardly to be reckoned as a disease unless the word is 
used in its most general application that includes any departure from 
normal structure or function. Neither of the two general classes 
into which diseases are usually divided, constitutional and parasitic, 
would include the leaf-cut. Though some of the cells are destroyed, 
the remaining tissues of the plant do not become abnormal in any 
way, and there is no indication that parasitic organisms of any 
kind—bacteria, fungi, insects, mites, or worms—are involved. Another 
class of ecological disorders may need to be recognized, intermediate 
between physiological diseases and mechanical injuries or trauma- 
tisms. Leaf-cut is a disease only in the sense that frostbite, snow 
blindness, and other environmental injuries are to be considered as 
diseases. 
Young cotton plants are often subjected to extreme conditions 
during the early stages of growth, when the leaf-cut injuries occur. 
The leaves and roots are still close to the surface soil, where they 
ean be chilled at night and scorched in the daytime. Cold nights 
are sometimes looked upon as the cause of the injury, and may be 
an intensifying factor, but the sudden heat of a bright morning sun 
seems more likely to kill the cells of the young leaves than low tem- 
peratures during the night. Leaf-cut often affects late plantings 
long after the night temperatures have ceased to approach the freez- 
ing point. It has been noticed that exposure to a bright morning 
sun after a cold night will throw cotton seedlings temporarily into 
a wilted state, doubtless because the leaves lose water by transpira- 
tion faster than it can be absorbed by the chilled roots. Ueaf-cut 
seems to be especially prevalent under such conditions. 
That leaf-cut is in some way connected with exposure or wilting 
of the delicate tissues is also shown by the fact that the injuries are 
most severe and occur most frequently along radiating lines midway 
between the principal veins. These lines of greater susceptibility 
represent the most exposed parts of the upper surface of the young 
[Cir. 120] 
