Feb. 15. J9I5 Brachysm 389 



pressed, as in Plate LV, the stipule on the same side of the leaf shows a 

 corresponding enlargement.' 



That brachysm in cotton is confined to the fruiting branches is doubt- 

 less connected witli the fact that the fruiting branches have more direct 

 relations with the floral organs. On account of the definite dimorphism 

 of the branches of the cotton plant, no floral buds are produced on the 

 main stalks or the vegetative branches. A study of brachysm in cotton 

 seems to indicate that such variations represent intermediate stages or 

 combinations of floral and vegetative characters. Brachytic varieties 

 have leaves that are more like involucral bracts, and bracts that are 

 more like leaves than those of normal long-jointed varieties. From this 

 point of view it is easy to understand that leaves of the fruiting branches 

 would be more likely to show abnormal anticipations of the characters 

 of the floral bracts than the leaves of the vegetative branches or the 

 main stalks, for these have no floral buds and represent earlier stages 

 in the development of the plant. 



INDEPENDENT ORIGINS OF BRACHYTIC VARIATIONS 



It has been supposed that all of the "cluster" varieties of cotton 

 belong to the same botanical series, but in reality the possession of short- 

 jointed fruiting branches is not a reason for supposing that two varieties 

 are related. Brachytic variations are very frequent and have been 

 found in so many different species and varieties of cotton that the idea 

 of derivation by crossing with a brachytic ancestral type is unwarranted. 



Brachysm is not known as a normal character of any wild species of 

 cotton, but seems to follow as one of the results of domestication and 

 selection. The same is apparently true in other families of plants. 

 Brachytic variations have arisen independently in several different types 

 of peas, beans, squashes, melons, and other climbing and creeping plants. 

 It is in such plants that the abnormal nature of brachytic variations is 

 most obvious. Under natural conditions, short-jointed variations of 

 climbing plants would be placed at a still greater disadvantage than those 

 of shrubby plants like cotton or coff'ec. 



If brachytic variations be supposed to represent the formation of a 

 new character, as assumed in the mutation theory of De Vries, it is diffi- 

 cult to imderstand why the same character should arise suddenly in so 

 many different and unrelated types of plants. But if brachysm be con- 

 sidered as a defect or failure of normal heredity, it becomes easier to 

 understand that many kinds of plants might be subject to similar de- 

 rangements. That the brachytic tendencies should appear independently 

 in so many different genera and families of plants makes it reasonable 

 to look for a general interpretation of this class of abnormal variations. 



' A further account of these abnormalities, with iJRiires of some of the iotenncdtate forms of bracts and 

 leaves, may he found iu an earlier bulletin. (Cook.O. F. Heredity and cotton brecdinc. U.S. Dept. Agr. 

 Bur. Plant Indus. Bui. 356. p. 69-:^, tiR. 3-ij. pi. 4H^. 1913.) 



