Amer. Nat. 49: 547-561 (1915)
Inheritance of habit in the common bean.
John B. Norton, M.S.

Habit is the external form of a plant taken as a whole. It is usually described by a few general adjectives, such as erect, open, spreading, etc. However, to study the inheritance of plant habit, a detailed analysis of the real characters underlying habit must be made. It is usually found that the outer appearance of a plant, its habit, is the result of a combination of independent characters, units, the recombination of which by crossing often results in plants much altered in appearance from the parent varieties. Characters usually unimportant may be found of primary importance in the formation of plant habit.

An example of such inheritance of habit is found in one of Webber's pepper hybrids (6). A cross was made between Red Chili, a variety with many erect fine branches, and Golden Dawn, with few, horizontal, coarse branches, both being of medium size. In the second generation recombination and segregation of the three character pairs occurred, although not in strict Mendelian proportions. The important feature of the results, however, lies in the apparent creation of a giant and a dwarf type, not by the appearance of new units by mutation, but simply by the transference of the characters fine and coarse branches. Hybrids having erect, many and coarse branches were giants, while those having few, horizontal and coarse branches were dwarfs. Other combinations of these characters gave intermediate forms.


The conclusions that can be drawn from observations reported in the preceding pages are:

I. That plant habit in beans is largely determined by the presence or absence of three characters which have been designated by the letters A, L, and T.

1. A, the presence of axial inflorescence permitting an indefinite growth, of the main stem and main branches, and a terminal inflorescence causing definite growth.

2. The length of the axis L, an important factor controlling plant habit and probably governed by a series of two or more factors for a length L1, L2, etc., which behave after the fashion of Emerson's hypothesis for the inheritance of quantitative characters.

3. The climbing habit is due to a factor for circumnutation. This factor may be called T. The cause of the various degrees of the climbing habit has not been determined with any degree of certainty. The contorted stems of erect bush forms are probably caused by T.

II. The factors A, L and T may be present in any possible combination, giving rise to the various habit types of beans.

III. When the types are crossed among themselves they behave approximately after the manner sketched in Table II.

BIBLIOGRAPHY

  1. Emerson, R. A. Heredity in Bean Hybrids. Rpt. Agr. Exp. Sta. Neb. 17 (1904), pp. 34-43.
  2. Emerson, R. A. Inheritance of Sizes and Shapes in Plants. AMER. NAT., 44 (1910), pp. 736-46 (1910).
  3. Emerson, R. A. and East, E. M. Inheritance of Quantitative Characters in Maize. University of Nebraska Agr. Exp. Sta. Research Bulletin 2 (1913).
  4. Jarvis, C. D. American varieties of Beans. Cornell University Agr. Exp. Sta. Bulletin 260.
  5. Tracy, Jr., W. W. American Varieties of Garden Beans. U. S. D. A. Bureau Plant Ind., Bulletin No. 109.
  6. Webber, H. J. Preliminary Report on Pepper Hybrids. A. B. A. Reports, YII and VIII, p. 188.