26 



DIMORPHIC BRANCHES IN TROPICAL CROP PLANTS. 



the same stock of hybrids showed only long branches like the Kekchi 

 parent. Hybrids between Kekchi and McCall, on the other hand, 

 growing beside the Triumph hybrids, showed the short " cluster " 

 branches of the McCall parent veiy definitely in both localities, and 

 in approximately Mendelian proportions. In the equable tropical 

 climate of Guatemala a planting of the McCall cotton failed to give 

 any indication of the cluster habit that characterizes this variety in 

 the United States." 



The frequency with which the abnormal intermediate forais of 

 branches occur in all the different stocks of Egyptian cotton that are 

 now being grown in Arizona increases the practical importance of 

 this class of facts. The behavior of other types of cotton during 



the period of acclima- 

 tization has shown 

 that new conditions of 

 growth are able to dis- 

 turb the processes of 

 heredity and thus lead 

 to many abnormalities 

 of development and 

 often to the complete 

 sterility of the plants, 

 either through failure 

 to form any flower 

 buds or through the 

 abortion of all that are 

 formed. 



A^Hiether the produc- 

 tion of these abnor- 

 mally shortened 

 branches of the Egyp- 

 tian cotton is connected 

 with the transfer to new conditions is not so plain as in the case of 

 the abnormal transformations of fruiting branches into vegetative 

 branches, but it is quite possible that the two conditions merely repre- 

 sent the extremes of one long series of variations. In the Dale cotton 

 as grown near Yuma, Ariz., in 1909, the abnormal shortening and 

 abortive tendencies of the branches were much stronger in the plants 

 raised from imported seed than in those produced from seed raised 

 at Yuma in 1908. The larger and more luxuriant plants also showed 

 the greater tendency to abnormal shortening of the fruiting branches, 

 instead of the usual tendency to elongate and change to the vegetative 



« Cook, O. F. Suppressed and Intensified Characters in Cotton Hybrids, Bul- 

 letin 147, Bureau of Plant Industry, U. S. Dept. of Agriculture, 1909, p. 23. 

 198 



Fig. 1.— Diagram of a cotton plant with two vegetative 

 branches and numerous fruiting branches. 



