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Summary.The spacing between adjacent hairs in vegetative whorls of Acetabularia acetabulum (formerly A. mediterranea) was earlier reported as being quantitatively responsive to calcium ion concentration in the culture medium. We here report a quantitative response to the concentration of the calcium-chelator EGTA, in the opposite sense to the effect of calcium. (Increasing [Ca 2+] diminishes the spacing; increasing [EGTA] increases it.) The earlier work was interpreted in terms of control of the spacing by a putative reaction-diffusion mechanism in the cell membrane, in which a receptor R was activated by calcium-binding to initiate the process. We extend this interpretation by treating CaEGTA as an uncompetitive inhibitor of the effect of calcium on R. This leads to thermodynamic constants for CaEGTA binding to the CaR complex: A/-/~ =-250 _+ 60 kJ/mol; AS~ = -820 -+ 200 J/mol 9 K. Consistency of the concentration and temperature dependences reported here with the postulated dynamic mechanism increases the probability that this mechanism is correct.

This paper presents computer programs for adjusting the mechanical properties of 2-in. dimension lumber for changes in moisture content. Mechanical properties adjusted are modulus of rupture, ultimate tensile stress parallel to the grain, ultimate compressive stress parallel to the gain, and flexural modulus of elasticity. The models are valid for moisture contents from 8 to. 23 percent (assumed green value). Although test results can be adjusted for moisture content, such adjustments decrease in accuracy with increasing change in moisture content. For this reason, the specimens should be conditioned as closely as possible to the target moisture content prior to test. Description and Purpose 1. Background Lumber strength properties vary with changes in moisture content. This is recognized and addressed in standards such as ASTM D 245-84 (ASTM 1987) through the use of factors that adjust lumber properties for changes in moisture content. Recent studies have established that the D 245 procedures for adjusting lumber properties for changes in moisture content are not necessarily accurate or conservative. Details of this research effort are discussed in several references (Aplin and others 1986; Green and others 1990; Jessome and Bellusillo 1985; McLain and others 1984) and summarized by Green and Evans (1989). The objective of this paper is to present a series of computer programs that are based on these recent findings and may be used to adjust lumber properties. Matched sets of Douglas-fir and Southern Pine lumber of different sizes and grades were tested at four moisture contents (10, 15, and 20 percent and green) in several studies. Changes in the properties of modulus of rupture (MOR), ultimate tensile strength (UTS), ultimate com-pressive stress (UCS), and flexural modulus of elasticity (MOE) were modeled as functions of change in moisture content (Green and others 1986, 1990, in preparation a,b). 1 The resulting models are incorporated in the computer programs listed in the Appendix and discussed in this paper. Although test results can be adjusted for moisture content, such adjustments decrease in accuracy with increasing change in moisture content. Specimens should therefore be conditioned as closely as possible to the target moisture content prior to test. 2. Description of the Algorithm Two different types of algorithms that predict how lumber properties change as moisture content changes are incorporated in the programs-one algorithm for MOR, UTS, and UCS and another algorithm for MOE. The way each of these algorithms works is discussed in detail, beginning with the more complicated algorithm used for MOR, UTS, and UCS. Because the algorithm is basically the same for MOR, UTS, and UCS, we will use MOR to explain the algorithm. a. Algorithm for Modulus of Rupture Data resulting from the moisture content-strength 1 Modeling of the UCS-moisture content relationships was conducted by Dr. J. D. Barrett, University of British Columbia, Vancouver, following procedures similar to those used in the publications ...

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