DIMORPHIC BRANCHES OF CENTRAL AMERICAN RUBBER TREE. 31 



The application of branch dimorphism to the problems of weevil 

 resistance is not necessarily limited to early fruiting and determinate 

 habits of growth. ^Vhile early fruiting is undoubtedly an advantage 

 under the ordinary conditions of cotton-growing communities, it does 

 not necessarily follow that late-fruiting types of cotton will be per- 

 manently excluded from cultivation in all weevil-infested regions. 

 Late-fruiting varieties must always suffer worse, of course, when 

 grown with early varieties, but if the late-fruiting varieties were 

 grown exclusively by whole communities the disadvantage would be 

 less and might be avoided entirely if varieties were secured which 

 w^ere able to set a crop of bolls within a short time after the produc- 

 tion of flower buds began. As long as the weevils were left without 

 pollen to feed upon, and were thus unable to breed, the danger from 

 weevils would not be increased. A quick-fruiting late variety, grown 

 by itself, would have the same advantages of weevil resistance as an 

 early variety growm under ordinary conditions, and with the prospect 

 of being able to set a larger crop of bolls than the small plants of 

 an extra-early variety. 



DIMORPHIC BRANCHES OF THE CENTRAL AMERICAN RUBBER 



TREE. 



The differences between the two kinds of branches in the Central 

 American rubber tree (Castilla) correspond in some respects to those 

 of the cotton plant. All the flowers and fruits are borne by one kind 

 of branches, while the other kind has vegetative functions only, like 

 the main trunk of the tree. But wdth regard to the origins of the 

 two kinds of branches, the rubber tree is directly contrasted with 

 the cotton plant. The fertile branches of Castilla always come 

 from axillary buds, while the vegetative branches are always extra- 

 axillary. 



The diversity of function is carried a step farther than in the 

 cotton plant, for the fertile branches do not become a permanent 

 part of the tree. After they have borne tw^o or three crops of fruit 

 they separate neatly from the trunk and drop out of their sockets, 

 which soon heal over. The dimorphic nature of the branches of the 

 genus Castilla and the self -pruning habit of the fruiting branches 

 have been described and illustrated in a former publication." 



Except in very rare instances, the fruit-bearing branches of Cas- 

 tilla remain quite simple and produce only leaves, followed in the 

 next year by a cluster of flowers above each of the leaf axils. Orowth 

 takes place only at the end of the branch, leaving a longer and longer 



« Cook, O. F. The Culture of the Central American Rubber Tree. Bulletin 49, 

 Bureau of Plant Industry, U. S. Dei)t. of Agriculture, 1003, p. 20, pi. 10. 

 198 



