396 Journal of Agricultural Research voi. m. No. 5 



evidently not true of brachytic variations of cotton. While it may be 

 that the mutations of other plants do not show changes in so many char- 

 acters in connection with brachysm, the general fact seems to be that 

 mutative changes affect several characters at once, instead of one charac- 

 ter alone. It is possible, of course, to disregard the other differences and 

 thus simplify the discussion of the Mendelian phenomena by giving 

 exclusive attention to single differences, but many of the statements that 

 have been made give a very misleading idea of the nature of mutative 

 variations.' 



In normal cotton plants there are sharp contrasts in length between the 

 intemodes that form the joints of the fruiting branches and those that 

 form the pedicels of the flowers, just as there are definite differences in 

 form and structure between the foliage leaves and the specialized leaves 

 that constitute the involucre. In brachytic varieties these contrasts 

 become less marked. The changes of characters are all in the direction 

 of reduced specialization of intemodes. Instead of the normally con- 

 trasted expression of the characters of the different kinds of intemodes 

 represented in the normal branches and floral parts, there is a reduced 

 contrast or intermediate expression of the characters, resulting in the 

 formation of abnormal intemodes. Variations of this kind, resulting 

 from intermediate expressions of characters that are normallv distinct or 

 separate in expression, may be described as metaphanic variations. 

 These would form a general class of abnormalities to include brachysm 

 and other similar aberrations of heredity. 



BKACHYSM AND HOMOEOSIS 



The nearest approach to a recognition of metaphanic variations as 

 representing intermediate expression of characters, as a general factor in 

 heredity, is probably to be found in the theory of translocation of char- 

 acters, or homoeosis, brought forward a few years ago by Dr. R. G. 

 Leavitt. The theory of homoeosis is that "a character or a system of 

 organization which has been evolved in one part of the body is transferred, 

 ready-made, tc another part." - 



The theory of homoeosis might be applied to the phenomena of 

 brachysm in cotton by considering that a partial translocation or homoeo- 

 sis had taken place, for the characters of the intemodes, leaves, and 

 involucral bracts are intermediate. The leaves become more bractlikc, 

 the bracts more leaf-like. But to represent typical cases of homoeosis 

 the leaves would need to be replaced by bracts or bracts by leaves, the 



' " The difference between a tall and s dwarf |)ea is not the same as the difference between a tall and a 

 dwarf man. In a human dwarf everyUiins is on a smaller scale than in the normal man. But a dwarf 

 pea is not simply a miniature edition, as it were, of a tall one — it differs from a tall pea in one single clur- 

 acteristic, the length of the intemodes, i. e., the sections of the stem between two nodes, or joints, where the 

 leaves are given off." Darbishirc, A. D. Breeding and the Mendelian Discover>'. p. 13-ij. London, 

 New York, 1911. 



' Leavitt, R. G. A vecrtativc mutant, and the principle of homeosis in plants. In Bot. Gar., v. 4;, 

 no. r, p. 64. 1909. 



