Developmental Instability in Leaves and Flowers of NICOTIANA TABACUM.

O R G A N S which are periodically repeated in plants show a more or less quantitative variation in spite of being governed by the same genotype. This variation is considered to be due, in addition to local fluctuation in environmental conditions outside and/or inside the plant body, to mistakes in the developmental course of organs resulting probably from the intrinsic nature of the organisms. That the magnitude of such quantitative variability of a given organ is genotype-dependent and susceptible to selection pressure has been demonstrated experimentally for the lateral asymmetry of sternopleural chaeta number in Drosophila (MATHER 1953; REEVE 1960, and other publications). In plants, Nicotiana rustica was used for the study of within-line variability in plant height, flowering time, leaf length and number of capsules per plant ( JINKS and MATHER 1955) or the study of intra-individual variability of stamen and pistil length and leaf shape (PAXMAN 1956). It was concluded from those investigations that the within-genotype variability in those characters was again genotype-dependent. The intragenotypic variability of quantitative characters which is considered to result from errors in developmental processes, though it might involve effects of undiscernible environmental influences, is called developmental instability, a phenomenon interesting from the viewpoint of genetics and evolution. For example, developmental instability in some traits of a panicle of rice induced SAKAI and SHIMAMOTO ( 1965) to investigate developmental relationships among them. It is also of great interest to inquire into what role developmental instability might play in adaptation, survival or fitness as well as production of higher organisms. For the last few years, the writers have conducted a few experimental studies on developmental instability in foliar and floral organs of Nicotiana tabacum L. This paper deals with the results of those studies which were carried out under the financial support of Japan Monopoly Bureau, to which our thanks are due.