824 
Journal of Agricultural Research 
Vol. XXVIII, No. 3 
RELATION OF GROWTH DISORDERS TO COTTON BREEDING 
The reactions of varieties to the growth disorders undoubtedly must be consid¬ 
ered as factors of adaptation. Susceptibility or immunity to a disorder might 
easily determine the success or failure of a variety in any district or region of pro¬ 
duction. Some of the types apparently are completely immune to disorders that 
in other types cause extensive and destructive malformations. 
The changes that may be caused in the characters and appearance of the plants 
by even the less serious disorders will need to be understood by those who take 
part in the breeding of varieties and the roguing of seed-stocks. The sporadic 
occurrence of such a disorder as crazy-top in scattered individual plants would 
give much the same impression as a mixture of varieties or a frequency of rogues 
or off-type plants, and might lead to the rejection of a superior seed-stock in the 
belief that it had “run out” or had been allowed to cross with other varieties. 
The growth disorders may explain why fields of cotton raised from the same stock 
of seed may sometimes show widely different degrees of diversity. 
Other disorders may exist, less frequent or less definite than crazy-top, and 
bring serious complications into the work of the breeder. The occurrence of 
such disorders might be very irregular, not only sporadic as to place, but also in¬ 
termittent in time or seasons. Conditions that had no relation to the growth of 
cotton might determine the existence of such diseases in malvaceous weeds or in 
other wild plants of adjacent lands, while other conditions would determine the 
presence or absence of insects to carry the disease from the native plants to the 
cotton. 
In bulk plantings an intermittent growth disorder might be confused with a 
Mendelian recessive character, which would not appear in the first generation of a 
cross, but would recur in the second and later generations. A disorder that did 
not reappear in the second generation might be considered a mass variation. 
Such outbreaks of brachysm, fasciation, or leaf-deformities are sometimes re¬ 
ported, but generally are disregarded by investigators, for lack of any rational 
explanation. In selection and roguing work with cotton it has been observed 
that two or more of the off-type plants are likely to be found together or close at 
hand, instead of being scattered indiscriminately through the fields. While seeds 
of the same boll might remain together, such tendencies toward grouping of the 
abnormal plants should be considered as indications that growth disorders may be 
involved. 
Study of aberrant plants that occurred in spots might lead to a recognition of 
other scattered plants as representing the same type of abnormality, allowance 
being made for the diversity that often exists among the individuals affected by a 
growth disorder. Also it is possible that growth disorders may have very mild or 
scarcely appreciable symptoms under moderate weather conditions early in the 
season, and that the serious distortion symptoms may appear abruptly at a later 
stage, when stress conditions occur. 
SUGGESTIONS FOR FURTHER STUDY 
With the recognition of crazy-top as a growth disorder, several new lines of 
investigation are suggested. The increasing substitution of Upland cotton for 
Pima in the Salt River Valley may facilitate the investigation of crazy-top, as 
well as increasing the importance of the disease, because the injuries are more 
severe in Upland cotton. Careful comparisons should be made where Pima and 
Upland cotton are affected by crazy-top under the same conditions. In view of 
the indications of more serious injury to the Upland plants, it is important to 
