12 CIECULAR NO. 109, BUREAU OF PLANT INDUSTRY. 



buds of the main stalk. The tunctional specialization, of the branches 

 oi the cotton plant is much less complete than in coffee and cacao, 

 where one form of branches is unable to regenerate the other form. 



A SYMPODIAL THEORY OF THE FRUITING BRANCHES. 



Another interpretation, advanced by Mr. H. M. Leake, of Cawn- 

 pore, India, makes the two kinds of branches appear much more 

 fundamentally different. According to Leake the vegetative 

 branches are monopodial and the fruiting branches sympodial. 

 This means that a vegetative branch is looked upon as a single con- 

 tinuous shoot, while a fruiting branch is supposed to be composed of 

 a succession of independent shoots, each represented by a single 

 internode and terminated by a flower. Thus, the floral buds of the 

 joints of the fruiting branches would correspond to the terminal buds 

 of the vegetative branches or of the main stalk. 1 



The structure of the fruiting branches and the nature of the dif- 

 ferences between the two kinds of branches are matters of special 

 interest, because Leake has reported Mendelian reactions in crosses 

 between varieties with different habits of branching. Varieties with 

 many vegetative branches on the main stalk are described as mono- 

 podial, while the varieties with only a few vegetative branches are 

 called sympodial, and the two characters are supposed to reappear 

 in definite proportions of the hybrid progenies. These results have 

 been accepted by Bateson and used as one of the chief illustrations 

 of the practical importance of the Mendelian methods of breeding 

 hybrid varieties. 2 



INFLUENCE OF ENVIRONMENT ON HABITS OF BRANCHING. 



The same characters that have appeared to Mendelize in India 

 have shown in the United States a wide range of environmental 

 modification. Varieties that would be considered sympodial under 

 some conditions become altogether monopodial under other condi- 

 tions. When the conditions keep the plants small, only a few of the 

 vegetative branches are produced or none at all; but when the con- 

 ditions favor luxuriant growth the fruiting branches may be replaced 

 or transformed into vegetative branches. Even under the same con- 

 ditions in other respects it is possible to control the development of 

 the branches by different methods of thinning. Plants that are 

 thinned early, so as to stand far apart during the earlier stages of 

 growth, are likely to show a much greater development of the vege- 

 tative branches than plants that are left closer together. In some 

 varieties of cotton the number of vegetative branches may be in- 



i Leake, H. M. Studies in Indian cotton. Journal of Genetics, v. 1, p. 205, 1911. 

 2 Bateson, W. Genetics. Popular Science Monthly, v. 79, p. 319, 1911. 



[Cir. 109] 



