BRACHYSxM, A HEREDITARY DEFORMITY OF COTTON 

 AND OTHER PLANTS 



By O. F. Cook, 

 Bionomist in Charge of Acclimatization and Adaptation of Crop Plants and Cotton- 

 Breeding Investigations, Bureau of Plant Industry 



The word "biachysm" is suggested as a name for abnormal variations 

 of plants characterized by shortening of the intemodes, without corre- 

 sponding reductions of other parts. Brachysm is to be distinguished 

 from nanism, or true dwarfing, which involves proportional diminutions 

 of many parts, if not of all. Genuine dwarfs, with consistent reductions 

 of all of the organs of the plant, would have little value for agricultural 

 purposes, but man}' brachytic varieties are highly prized. In spite of 

 their shorter intemodes, brachytic varieties often bear leaves, flowers, 

 and fruits as large as plants of normal stature, and sometimes larger. 

 Most of the so-called "dwarf," or "bush," varieties of peas, beans, 

 squashes, tomatoes, and other garden vegetables represent brachysm 

 rather than true dwarfing. The "cluster" and "limbless" varieties of 

 cotton belong to the same category, and the vSan Ramon coffee of 

 Costa Rica affords another example of brachysm in a woody plant. 



A special interest may be claimed for the cluster and limbless varieties 

 of cotton because they seem to throw light on the nature of brachj'sm 

 and similar abnormalities as phenomena of heredity. As brachytic 

 varieties arise by nuitation and show allernative inheritance in crosses, 

 they illustrate two of the jjlienomena of heredity that have received much 

 attention in recent years. The morphological and physiological relations 

 of such characters must be understood before it is possible to appreciate 

 their practical importance in breeding or their bearing upon general 

 evolutionary problems. 



SPECIAL FEATURES OF BRACHYSM IN COTTON 



The special interest that attaches to the phenomena of brachysm in 

 cotton arises from two general facts: That the shortening of the inter- 

 nodes is usually confined to the fruiting branches and that it is usually 

 accompanied by other abnormalities. On account of the specialized 

 structure of the cotton plant, it becomes possible to learn more of the 

 relations of brachysm to other phenomena of heredity than if all of the 

 intemodes of the plant were affected and the other organs remained 

 unchanged. 



Journal of Agricultural Research, Vol. IH, No. 5 



Dept. of AKriruItllrr, Wn«;hincton, D. C. Keb. 15. 1Q15 



O 40 

 (387) 



