Use of Photocopying for Non-Destructive Leaf Area Measurements Planar measurements of area are frequently required for very diverse applications. General methods include planimetry, grids, dot counting, established correlation formulas, shadow or photographic prints, and various area meters.',2 In our work an plant growth and metabolism, it is often necessary to determine leaf shape as well as area. To study continuous growth and change in development, the method of measurement must he applicable to intact plants, nondestructive, and should provide a permanent record of linear dimensions. Preferably, the method should also be adaptable to fragile leaves of intricate shape and variable size, e.g., the compound leaf of tomato. A method combining general practices used in blueprinting and photocopying serves very well for this purpose. The method consists of four steps. The first steputilizes astage made from two Plexiglas" sheets separated at the corners by small squares of 1.3-mm thick foam mounting tape to hold a sheet of standard weight Diazo paper (8'12 X 11 in. blueprint, rapid speed 11).An additional Plexiglas sheet, hinged a t one end to the other two and spaced appropriately with foam tape (3.9 mm), is placed over the undetached leaf. After the leaf is positioned, hayonet forceps (ex., Lucae ear forceps) can he used to gently separate any overlapping or curled leaves. Diazo paper is inserted and subsequently exposed with a photospot lamp (G.E. PHIRSP 2,500 W) applied from a fixed distance of 12-15 in. above the stage for 10-15 s until the paper blanches. Second, the leaf print is developed in a hood by passing an inverted glass funnel connected with tubing to a tank of NH3 gas over the exposed paper. If NH3 gas is not available, aprint may be heldover ashallow dish ofeoncentrated NH40H for development. Third, a photocopy (e.g., Kodak Ektaprint 150 copier-duplicator) is made of the leaf print to provide a clean, permanent record. From the photocopy, a final print is reproduced on a transparency (e.g., Kodak Ektaprint). Fourth, from the transparency mint. area measurement is obtained hv a mid. olanimetrv. or an area meter. In our use. measurements from the transnarencv area meter. Since lamp intensity decreases with use, replacement of the lamp in the system will require adjustment of either the exposure time (decreased) andlor distance above the stage (increased) in order to maximize the clarity of the print and to avoid thermal damage to plant tissue due to the increased intensity. Our measurement of leaf temperature, under the described conditions, indicates a maximum expected increase of 5 - 6 T during exposure.
Reference to a company andlor product named hy the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable. Marshall, J. K., Photosynthetica, 2,41 (1968). Kyet, J., and Marshall, J. K., "Plant Photosynthetic Production. Manual of Methods," (Editor.Sestak, Z.), Dr. W. Junk N.V. Publishers, The Hague, 1971, p. 517.
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Marian L. Lyman Donald E. Campbell J. Corse Western Reoional Research Center Agricultural Research Service U.S. Department of Agriculture Berkeley, CA 94710 ~
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42
Journal of Chemical Education
