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Abstract: Studies in Agaricus bisporus demonstrated that the lamellae control stipe elongation and cap trama expansion. Neither stipe nor cap trama can take over this role. After decapitation the rate of stipe growth decreases sharply, but reaches zero only at 3-4 days after the operation on fruit bodies of over 2 cm length. This residual growth indicates that a growth factor which remains in the stipe is gradually used up. Lamellae alone, or parts of the cap with lamellae left attached at one side of the stipe induce negative stipe curvature. Production of a growth-promoting substance by the lamellae was demonstrated by strong negative curvatures of decapitated stipes caused by asymmetrical application of agar blocks with diffusâtes from small amounts of lamellae. Application of test blocks to the intact lateral surface of decapitated stipes was found to be the best technique. Since carefully washed agar gives small negative stipe curvatures due to the water in the agar, control blocks of plain agar must be applied to the stipes opposite the test blocks. A test with blocks placed on the apical cut stipe surface was unsatisfactory since the diffusâtes only slightly promoted growth as compared to controls. Application of test blocks to symmetrical cap remnants without lamellae gave no, or erratic stipe curvatures; probably the active substance is absorbed by the trama itself. When applied to the stipe sides, diffusâtes gave significant negative curvatures if diluted a hundred times, but not if diluted a thousand times. Diffusâtes from small amounts of cap trama were inactive.
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