DIMORPHIC BRANCHES OF THE COTTON PLANT. 13 



unable to bear flowers or fruit. Branches that bear fruit may be 

 correspondingly restricted on the vegetative side. Different species 

 and varieties of plants are so unlike that no general principle of 

 classification can be applied except that of distinguishing between 

 the different foims of specialization. 



The most useful distinction between limbs and other forms of 

 branches relates to differences of function rather than to the structure 

 or positions of the parts. In the cotton plant, for example, the 

 axillary branches function as limbs, while in the Central American 

 rubber tree they are definitely specialized for fruiting and do not 

 become pennanent parts of the tree. They die and drop off after 

 they have borne two or three crops of fruit. 



The branches that arise from extra-axillaiy buds also have their 

 functions reversed in the two cases. In the rubber tree the extra- 

 axillary buds produce limbs but no fruiting branches, while in the 

 cotton plant all the fertile branches arise from extra-axillary buds. 



DIMORPHIC BRANCHES OF THE COTTON PLANT. 



Though the dimorphism of the branches of the cotton plant is not 

 an extreme case, it may be better to use it as the first example before 

 considering the other tropical plants that are less known in the TTnited 

 States. The differences are more striking in some of the tropical 

 plants, but are no more significant in their agricultural bearings. 

 The distinctions between the two kinds of branches of the cotton 

 plant depend upon position and function rather than upon any very 

 conspicuous differences of form or structure. This may explain why 

 the dimorphism of the branches has continued to be overlooked in so 

 familiar a plant as the cotton, although the difference between ordi- 

 nary short fraiting branches and large basal branches or " wood 

 limbs " is obvious at a glance and is familiar to all planters." 



The cotton plant, as represented by the Upland varieties in general 

 cultivation in the Southern States, consists of a central axis or 

 " stalk " bearing a leaf at the end of each joint or intemode. 

 Branches that arise from the axils of the leaves do not normally 

 bear fruit, but behave like divisions of the main stalk. A fertile 

 branch arises at one side, right or left, of an axillary branch or an 

 undeveloped axillary bud which may give rise to an axillary branch 

 late in the season. The position is usually constant throughout in 

 the same stalk, so that the plants can be distinguished as right-handed 



° For a brief statemeut regarding dimorphism of branches in cotton, see " Wee- 

 vil-Resisting Adaptations of the Cotton Plant," Bulletin 88, Bureau of Plant 

 Industry, U. S. Dept. of Agriculture, I90G, pp. 19-20. See also "A Study of 

 Diversity in Egyptian Cotton," Bulletin 156, Bureau of Plant Industry, U. S. 

 Dept. of Agi-iculture, 1909, pp. 28-30. 

 198 



