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Di chuyển từ các nước với đất, thực vật phát triển những đặc điểm cho phép họ để đối phó với môi trường mới của họ. Có thể cho rằng, vấn đề đáng kể nhất mà họ phải đối mặt với khô tương đối của không khí. Mất nước nhanh chóng từ các mô quang hợp yêu cầu cung cấp nước bằng nhau nhanh chóng. Khả năng vận chuyển nước nghèo hạn chế đầu tiên nonvascular thực vật kích thước nhỏ [1]. Sự phát triển của chất gỗ bao la tăng thủy lực dẫn và góp phần vào việc đa dạng hóa quy mô nhà. | 4 Murray s Law and the Vascular Architecture of Plants Katherine A. McCulloh and John S. Sperry CONTENTS 4.1 Introduction.85 4.2 Murray s Law.86 4.3 Applying Murray s Law to Xylem.88 4.4 Importance of the Conduit Furcation Number F .90 4.5 Does Xylem Follow Murray s Law .91 4.6 Does Tree Wood Not Follow Murray s Law .92 4.7 Nature of the Mechanical Constraint on Hydraulic Efficiency.94 4.8 Da Vinci s Rule.95 4.9 Developmental and Physiological Constraints on Transport Efficiency. 95 4.10 Comparative Efficiency of Conifer vs. Angiosperm Tree Wood . 96 4.11 Conclusions.97 Acknowledgments.97 References.97 4.1 INTRODUCTION In the move from the water to land plants evolved traits that allowed them to cope with their new environment. Arguably the most dramatic problem they faced was the relative dryness of air. Rapid water loss from photosynthetic tissues requires equally rapid water supply. Poor water transport capabilities limited the earliest nonvascular plants to small size 1 . The evolution of xylem vastly increased hydraulic conductance and contributed to the diversification of plant size evident today 2 3 . Xylem structure has changed and diversified considerably over time presumably reflecting progressive adaptation 4 . Measuring this adaptation is a challenge because it is not always obvious what traits are being selected for and what constraints and trade-offs are limiting trait evolution. It seems likely however that a universally favorable trait for a water-conducting network is maximum hydraulic conductance per unit investment. Higher hydraulic conductance means greater volume flow rate of water per pressure drop across the network. The higher the hydraulic 85 Copyright 2006 Taylor Francis Group LLC 86 Ecology and Biomechanics FIGURE 4.1 A bifurcating blood vessel for which Murray s law is derived in the text. Shown are the radii r and lengths l of mother subscript 0 and daughter subscript 1 branch ranks. conductance the more leaf area that can be supplied .
