Access

You are not currently logged in.

Access JSTOR through your library or other institution:

login

Log in through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Annual Versus Biennial Growth Habit and Its Inheritance in Melilotus alba

Hugh Burnice Smith
American Journal of Botany
Vol. 14, No. 3 (Mar., 1927), pp. 129-146
Stable URL: http://www.jstor.org/stable/2435604
Page Count: 18
  • Read Online (Free)
  • Download ($12.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Annual Versus Biennial Growth Habit and Its Inheritance in Melilotus alba
Preview not available

Abstract

As determined from a classification of 2042 individuals, all of which were progeny of self-pollinated heterozygous plants, the difference between annual and biennial habits of growth in white sweet clover is due to a single gene difference in the germ plasms of the two varieties. Therefore, a single gene determines the difference in the duration of life of the two varieties of Melilotus alba. This gene determines time of maturity and is not concerned with the dormant period between vegetative growth and fructification. Because of the close relationship between length of growing season and habit of growth in Melilotus alba, a genetic change, a mutation, determining time of maturity may have brought about the assumption of the annual habit in this species. It is not known whether the annual white sweet clover originated by mutation from the biennial form; but if it did, it is considered to represent a progressive evolutionary change which has taken place under natural conditions. The evidence presented in this paper of a single gene difference between the germ plasms of annual and biennial Melilotus alba, together with the recorded history that the annual is of more recent origin than the biennial, seems to favor the view that the annual form of this species has originated by mutation from the biennial form. If, as seems to be the case, the origin of the annual was by mutation, we have an interesting addition to the list of dominant mutations. The origin of annual from biennial and perennial habit and of biennial or annual from perennial habit in many lines of descent is probably to be explained by mutation. These changes, in view of their apparently high frequency in evolution, may be expected to show simple inheritance. There is a high correlation between the habit of growth and the length of the growing season of the species of Melilotus in nature, which conforms to the ideas of Türesson regarding the natural selection of ectotypes. Biennial white sweet clover is functionally an annual, in that it is capable of flowering on the primary stems of the first season if the period of growth is sufficiently prolonged. It is likewise from a structural standpoint a typical biennial in that it has morphological provision, in its crown buds, for the completion of its life cycle in the second season if (as is always the case in the North) the stems of the first season do not reach maturity. Annual white sweet clover differs from the biennial most obviously in the shorter period required for maturation. This physiological peculiarity is found to be correlated with a larger cell size in corresponding tissues, which may in turn, if Tinckler's ideas are correct, be associated with a difference in metabolism. (The biennial and annual forms would provide ideal material for a test of the metabolism hypothesis.) Since the biennial habit of Melilotus alba is facultative, it follows that the present paper is primarily a study in the inheritance of duration of life. That a normal difference in duration of life of such great magnitude should be inherited as a simple Mendelian character is a most striking fact.

Page Thumbnails

  • Thumbnail: Page 
129
    129
  • Thumbnail: Page 
130
    130
  • Thumbnail: Page 
131
    131
  • Thumbnail: Page 
132
    132
  • Thumbnail: Page 
133
    133
  • Thumbnail: Page 
134
    134
  • Thumbnail: Page 
135
    135
  • Thumbnail: Page 
136
    136
  • Thumbnail: Page 
137
    137
  • Thumbnail: Page 
138
    138
  • Thumbnail: Page 
139
    139
  • Thumbnail: Page 
140
    140
  • Thumbnail: Page 
141
    141
  • Thumbnail: Page 
142
    142
  • Thumbnail: Page 
143
    143
  • Thumbnail: Page 
144
    144
  • Thumbnail: Page 
145
    145
  • Thumbnail: Page 
146
    146