808 
Journal of Agricultural Research 
Vol. XXVIII, No. 8 
tion of the edges of the wounds. Adhesions may be formed in the scars and 
are the cause of some of the distortions of the mutilated leaves. 4 
Tomosis is of general occurrence in all of the cotton-growing districts of the 
United States, as well as in foreign countries. Though extensive tomosis injuries 
are usually confined to the seedling stage of the plants, a few injured leaves are 
usually to be found at later stages of growth. Occasional individuals show many 
tomosis mutilations through the season, and such plants are likely to be sterile 
or abnormal in other ways. Similar cases of congenital tomosis are likely to be 
found in hybrid stocks as one of the abnormalities that appear in the second and 
later generations. Also it appears that tomosis is more frequent in plants that 
are affected wdth other growth disorders than in normal plants under the same 
conditions. 
The death of the leaf-tissue in tomosis has been traced to the oil-glands, which 
apparently are killed in advance of the neighboring cells. Under the microscope 
it is possible to see that the cells around the oil-glands are injured before they are 
killed. The chloroplasts become discolored and then disintegrate and dis¬ 
appear, leaving the cells transparent. Along the edges of the wounds some of 
the injured cells survive, but with no green color, the loss of the chloroplasts being 
permanent (PI. 5, B, C, D). The injury to the chloroplasts suggests an analogy 
with the mosaic diseases, though the course of the disease is very different. The 
tomosis injuries are much more acute but more definitely limited, and with no 
subsequent weakness around the injured areas of leaf-tissue. 
Though tomosis is very frequently accompanied by another disorder called 
hybosis, or leaf-curl caused by plant lice, which also affects cotton in the seedling 
stage, tomosis injuries may be severe where there are no plant lice, and no 
relation to other insects has been found. That the occurrence of tomosis is so 
general in itself is a reason for supposing that the injuries are not due to a parasite 
but are a general effect of some unfavorable condition, such as the wider and 
more sudden changes of temperature to which the young plants are exposed 
during the early stages of growth. 
When tomosis is severe the growth of the seedling is retarded, and the terminal 
bud may be aborted, so that the plants are crippled and deformed, and generally 
produce fewer bolls than their normal neighbors. Except in these cases the ef¬ 
fects of tomosis appear to be strictly temporary. Though all of the plants 
in a field may be badly affected, with the early leaves badly mutilated and de¬ 
formed, such a period of distress may be followed by a general and rapid recovery 
with all of the new growth quite normal, as soon as the weather is favorable. 
(See PL 5, A.) 
If the plants are not thinned too early the injured individuals are easily recog¬ 
nized and removed. Also there is less exposure to extreme conditions if the young 
plants are close together in the rows. 
Tomosis occurs in all of the principal types of cotton, though some are more 
susceptible than others. In Arizona and California the Pima cotton usually is 
appreciably less susceptible to tomosis than the Upland varieties. Earlier 
recovery of Pima cotton from tomosis no doubt is connected with its ability to 
grow at lower temperatures. The Upland varieties remain dormant for a longer 
period while the weather is cold and also lose more time in the stage of suscepti¬ 
bility to tomosis. 
With Pima and Sea Island varieties growing under the same conditions, at 
Sacaton, Ariz., the tomqsis injuries of Sea Island cotton are more serious and 
« Cook, O. F., leaf-cut or tomosis, a disorder of cotton seedlings (4). See also Reports of the 
Chief of the Bureau of Plant Industry, U. S. Department of Agriculture ( 10 , 11 , 13 , 16 ). Cook, O.F., 
Results of cotton experiments intl911 ( 2 ). 
