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Journal of Agricultural Research 
Vol. XXVIII, No. 8 
the club-leaf disorder in China, where all of the plants became affected in the 
latter part of the season, and all of the late-season growth was abnormal. 
The irregular and interrupted distribution of crazy-top would seem to indicate 
that the disease is spread by insects or other agents that are not continuously 
present in the fields, or all of the plants would be affected, as in the cyrtosis 
disorder in China. The distributor may be active in the spring and fall but 
not in midsummer, as with the plant lice which cause the leaf-curl disorder. 
In the Hartgville cotton field at Casa Grande some of the plants had been 
dwarfed at very early stages and were only 6 or 8 inches high at the end of the 
season. Around these were other badly crippled plants, but of larger size, 15 
to 18 inches high. Finally, there were many plants that had grown to full 
size, with a height of 3 to 4 feet, and produced normal bolls, although the late- 
season top growth was definitely abnormal. Thus it seemed that three stages 
or periods of infestation might be indicated in this field. 
The irregular mode of occurrence of crazy-top also appears inconsistent with 
the idea of genetic or physiological causes. A genetic defect would be scattered 
generally through the fields in the same way as other off-type individuals, or 
“rogues/’ while physiological effects would be expected to show more definite 
grouping and more continuous gradations, but the facts do not accord with 
either of these assumptions. While crazy-top appears under a wide range of 
conditions, there are many fields that show no crazy-top. 
In order to test heritability of the disorder, seed was saved in 1923 from indi¬ 
viduals having pronounced symptoms of crazy-top, and progenies are being 
grown in 1924. Also seed was saved from scattered rogues or off-type plants 
of the Pima, Acala, and Hartsville varieties, and the progenies are to be studied 
with a view to the possible relations with crazy-top. 7 
Of course it is not possible to have a clear understanding of the distribution 
and occurrence of such a disease until the causes are discovered, including the 
sources of infection and the insects or other agents for conveying the virus from 
one plant to another. The usual plant lice of cotton may be the conveyors 
of crazy-top, or leaf-hoppers, thrips, mites, or nematodes may be implicated. 
CRAZY-TOP UNDER DIFFERENT CONDITIONS 
The disorder is not restricted to a particular type of soil or to other special 
conditions, though the severity of the symptoms and the extent of injury depend 
largely upon the conditions. The occurrence of the disorder must not be con¬ 
fused with the extent of injury. If only the extreme cases were noticed one 
might suppose that the disease appeared only with bad conditions, but crazy- 
top plants are also found under the most favorable conditions, where the plants 
that are not affected show the most normal development and produce the 
largest crops. It should be remembered that shedding, sterility, and abnormal¬ 
ities of branching also occur in plants that are over-luxuriant; and that such 
symptoms may be induced by alternate checking and forcing of growth, as may 
occur in rich soils which are too heavy to take water readily or have too light a 
subsoil to hold water from one irrigation to another. Under such conditions 
the stalks may continue to grow though most of the fruiting branches are aborted. 
If no extreme conditions were encountered, the recognition of such a disease 
would be the more difficult, since the effects might be limited to a slight depres¬ 
sion or subnormal status of the affected plants, scarcely to be distinguished from 
7 A report from C. J. King, under date of June 12, 1924, shows that 132 hills were planted at Sacaton 
with seed from 14 crazy-top plants of Hartsville cotton, but only 3 hills germinated, all from the seed of 
one plant. Of Pima cotton, 140 hills were planted with seed from 13 abnormal individuals, and germina¬ 
tions were secured in 86 hills. Only 4 lots of the Pima seed showed no germinations. 
