MORPHOLOGY OF COTTON BRANCHES. 1 



By O. F. Cook, Bionomist in Charge of Crop Acclimatization and Adaptation 



Investigation*. 



INTRODUCTION. 



The cotton plant has two distinct kinds of branches, differing in 

 position, structure, and function. The upright "limbs," or vege- 

 tative branches, behave like the main stalk of the plant and do not 

 produce flowers or bolls. The floral buds appear on horizontal fruit- 

 ing branches. The specialized habits of growth are of interest from 

 the general standpoint of morphology, as well as in their applications 

 to cultural and breeding problems. The practical considerations 

 have been- treated in several publications of the Bureau of Plant 

 Industry. 2 



POSITIONS AND HOMOLOGIES OF BUDS. 



The positional relations of the two types of branches have seemed 

 to throw the clearest light upon their structural homologies. It is 

 easier to determine the positions of the buds from which the branches 

 develop than to understand the relations of the mature branches. In 

 addition to the bud that serves to continue the growth of the shoot, 

 each internode of the cotton plant produces two other buds, one in 

 the axil of the leaf and another to the right or left of the axil. Some 

 stalks are right handed and others left handed with respect to the 

 position of the extra-axillary buds and the branches produced by 

 these buds. 



The axillary buds usually remain dormant, but may be developed 

 into vegetative branches when the conditions are favorable to luxu- 

 riant growth of the plants. The fruiting branch es arise from the extra- 

 axillary buds of the main stalk and the vegetative branches. The 

 floral buds are also developed in the extra-axillary position on the 

 fruiting branches. Thus the floral buds of the fruiting branches 

 have been considered homologous with the extra-axillary buds that 

 give rise to the fruiting branches. The axillary buds of the fruiting 

 branches are able to produce vegetative branches, like the axillary 



1 Issued Jan. 4, 1913. 



i Weevil-resisting adaptations of the cotton plant, Bulletin 88. A study of diversity in Egyptian 

 cotton, Bulletin 156. Dimorphic branches in tropical crop plants: Cotton, coffee, cacao, the Central Amer- 

 ican rubber tree, and the banana, Bulletin 198. Arrangement of parts in the cotton plant, Bulletin 222. 

 Dimorphic leaves of cotton and allied plants in relation to heredity, Bulletin 221. The branching habits 

 of Egyptian cotton, Bulletin 249. 



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