Abstracts of Papers - Harvard Forest - Harvard University

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ship between auxin concentration and H+ efflux (Rayle, 1973 - Planta), we postulate a mechanism for phototropism based on change in relative hormone con- centrations between opposite sides of these structures. WEBSTER, HAROLD J. Biology Department, DuBois Campus, The Pennsylvania State University, DuBois, PA 15801 - Elemental Analyses of Splachnaceae and Their Sub- strates. The elemental analyses of field-collected plants and their substrates and of laboratory-cultured plants of the Splachnaceae provided evidence in reference to the nitrophile hypothesis. The Splachnaceae exhibit strong affinities for substrates of animal origin, which has been suggested as a requirement for nitrogen. Owl pellets and dung with and without plants of the Splachnaceae had relatively high levels of N, P, and Ca. Field-collected taxa had slightly higher elemental percentages than other cold-region bryophytes. The higher Ca and P levels reflect substrate contents. Tetraplodon mnioides plants had higher Ca, P, and N percentages than did the more hydric Aplodon wormskjoldii plants. Anal- ysis of cultured plants shows no major differences among taxa or among media used, although deficiency levels were indicated for plants grown on media with low levels of Ca, N, and Mg. Comparison of field and culture analyses suggests field plants may be nitrogen deficient despite the high nitrogen content of their substrates. Symposium: A Developmental and Structural Perspective on Phenotypic Plasticity: A Contribution to its Delineation INTRODUCTION When the concept of phenotypic plasticity is invoked, it is usually in reference to the impact of external environments on plant form. There are two possible ways to view phenotypic plasticity. One is that it represents an additional set of developmental events induced by the external environment and, in that con- text, represents something added to the normal developmental processes in a plant. The other is that it is a manifestation of the normal developmental events seen in the ontogeny of any plant. It is the purpose of this symposim to present information on plant development, including that of phenotypically plastic systems, to assess which of the two views presented above, or any others, are most appropriate for understanding phenotypic plasticity. An understanding of the underlying basis for phenotypic plasticity is of significance in attempting to explain the evolutionary and developmental consequences of its existence. Organized by Jack Maze, University of British Colum- bia, Vancouver, BC. Developmental and Structural Section 9 WHITTIER, 1R. O., H. PRINGLE, H. A. MILLER & B. A. WHITTIER. Department of Biological Sciences, University of Central Florida, Orlando, FL 32816 - Matrix analysis for Pacific insular bryogeography. Electronic data files established during production of the Prodromus Florae Muscorum Polynesiae (1978) and the Prodromus Florae Hepaticarum Polynesiae (in press) provide a data base containing nomenclatural and distributional records for 174 genera and 1,760 hepatic species, and 254 genera and 1,627 moss species, reported on 114 tropical Pacific islands and as shared with 49 circum-Pacific and other world areas approximating those of Index Muscorum (Wijk et al ., 1959-1967). Files kept current on key-punched cards for security may be accessed directly by entry onto Harris 800 disk files. FORTRAN programs enable production of matrices as large as 200 X 200 geographic areas. Recoding permits organization into smaller condensed geographic groups or regions. These matrices display numbers of species reported for an island or its archipelago on the diagonal, and at matrix intersections in the upper triangle, numbers shared by two areas. A lower triangle contains indices of similarity. A taxonomic recoding option permits similar matrix production for genera. Subprograms list (1) families (either alphabetically or phylogenetically) with their genera and species, or (2) genera and species alone, for any single island, group, or for all islands and groups, and can ideritify and enumerate reported endemics and their percentage of the known bryoflora. Various cluster analysis routines carn be applied within the program system. Program construction design is such that application requires minimal computer experience, and permits use of other taxonomic and biogeographic data sets (up to 9,999 taxa and 200 geographic areas). Conversion to a microcompuiter program system is planned. DEVELOPMENTAL AND STRUCTURAL SECTION FISHER, JACK B. Fairchild Tropical Garden, Miami, FL 33156. - Branching patterns and simulations of trees: deterministic vs. stochastic models. Published attempts at computer modeling of the geom- try of tree crowns and rhizomes are reviewed. Deter- ministic and stochastic (probabilistic) models are contrasted, and the problems associated with each method of simulating complex biological patterns are noted. Small changes in the elemental parameters of branching geometry (branch angles, branch unit length) can have major effects on overall crown shape after many orders of branching. While stochastic simulations produce "realistic" trees, they may not be meaningful for ecological or adaptational studies since they obscure local specific phenotypic responses to environmental or age-dependent condi- tions, e.g. sun-shade effects, architectural reiteration. KAPLAN, DONALD R. Department of Botany, University of California, Berkeley, CA 94720 - Heteroblastic development and phenotypic plasticity in higher plants. Any effort to study environmentally induced changes in plant structure (phenotypic plasticity) must be done against the background of the normal develop-
10 Developmental and Structural Section mental changes expressed during the ontogeny of the plant. The term "heteroblastic development" has been used to refer to such regular ontogenetic changes in plant form. Using recent research on the developmental basis of the heteroblastic change in leaf form in Acacia, it will be shown that the change involves: 1) a regular ontogenetic change in proportion of blade to petiole; and 2) a change in the type of blade morphology (from pinnate to simple) which is independent of its position in the shoot and hence a plasticity response. Once a clear delineation of the involvement of these two components in this heterophylly is made, it can be shown that the original distinction between homo- blastic and heteroblastic development was falsely defined because it was based on the phenotypically plastic component. From an analysis of attempts to induce juvenile types of foliage in adult plants, using hormones such as gibberellic acid, it is suggested that many of the responses may be examples of phenotypic plasticity and not a true reversal of the developmental phase. The significance of these conclusions for the evaluation of hormone roles in phase changes in plants will be discussed. PAOLILLO, D. J., JR. AND GAIL RUBIN. Section of Plant Biology, Cornell University, Ithaca, NY 14853. - Environmental plasticity of sexual phenotypes in Onoclea sensibilis.. Young Onoclea gametophytes become male in abundance when grown on their native soil but are inhibited from expressing maleness when grown in axenic cultures on agar. Classical experiments designed to test the action of antheridiogens using agar-grown Onoclea gametophytes are logically restricted to the explanation of laboratory anomalies because the control plants do not resemble field-grown organisms. Most soil-grown plants become male, without the intervention of antheridiogens, after attaining their meristems and becomingsmall hearts. On agar, female- ness is more prominent but some heart-shaped gametophytes become male at the same time their cohorts become female. Thus, the concept that a meristem is antithetic to maleness is also related to laboratory artifacts. On agar, dark-grown gametophytes become male at the same time as light-grown gametophytes. Male plants in the dark are small filaments. Thus, neither the meristem nor the morphological state of the organism appears to bear a direct, causal relationship to maleness. Likewise, there is no basis for the concept that the action of antheridiogens in Onoclea is to overcome a light-induced block to maleness. It remains possible, however, that the action of applied antheridiogen is antagon- ized by light in Onoclea. However, these and all other conclusions based on agar cultures must be interpreted with a fuller knowledge of the limits of phenotypic plasticity when Onoclea is the test organi sm. Richards, J.H. Dept. of Biol., Fla. Inter- national U., Miami, FL 33199. Developmen- tal basis of leaf plasticity in Eichhornia crassipes Solms. (Pontederiaceae). In 1965 A.D. Bradshaw defined plasticity as the "amount by which the expression of indiv- idual characteristics of a genotype are chan- ged by different environments." Such change requires some change in development of that characteristic. Leaf development was studied in a clonal mat of water hyacinth in order to quantify parameters which show variability and to document the developmental basis of divergence in form. The mat environment var- ies from the mat edge to center. Leaves on plants inside the mat differ in petiole length, lamina length, petiole width and lamina width from leaves on the mat edge. Dif- ferences are not a function of plant age alone. Leaf shape parameters have different variances between the two environments--petiole measurements display more variability than lamina. When development of the two leaf types is compared, they show parallel relative growth rates for leaves less than 2.5 mm. Divergence in form results from differences between leaf types in 1) how long growth continues and/or 2) late-developing differences in relative growth rates. The earliest divergences in relative growth rates occur in leaves app. 8 mm long. Developmental divergences between these plastic leaf types contrasts with developmental divergences between invariant leaf types. In E. crassipes prophylls and foliage leaves are always different in form, regardless of environment. These differences, however, are present soon after leaf initiation. Symposium: Developmental Physiology of Flowering INTRODUCTION The process of flowering can be divided into at least five sequential phases; our speakers will re- view the subjects of flower induction, flower differentiation, flower opening, pollination, and flower senscence. Organized by Ross E. Koning, Rutgers University, Pis- cataway, NJ. GREYSON, RICHARD I. Department of Plant Sciences, University of Western Ontario, London, Ontario. N6A 5B7. - Flower primordia - a challenge to plant developmental i sts. The following phenomena, all described from traditional morphological and anatomical viewpoints still represent a profound challenge to developmentalists. A) Primordia initiation: The relative contributions and orientations of cell division and enlargement to the setting and establishment of a primordium. B) Determination and differentiation: A number of different models have been described. Some exhibit delayed canalization while others are less easily modified. C) Organ growth: From the few analyses that do exist, primarily on stamens, one should expect considerable variety in the regulatory stimuli and the type of cellular response which leads to common structures. This variety of mechanism points toward considerable parallalism in the evolution of the final developmental events. D) Sexual differentiation: The exploration of the developmental basis of sexual differentiation has proceeded at a plant of levels. Perhaps the most popular studies impl icate pl ant hormones as causal factors. In reviewing these studies we conclude that while in some flowers regulation may sharply correlate with endogenous levels and activities of hormones, more frequently such parallels cannot be identified.
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