Growth of the Photosynthetic Area of Citrus

Part I.-1. The growth of the photosynthetic area of Valencia orange trees has been determined from the total number and blade lengths of leaves from four trees of 3, 6, 12, and 29 years of age. The frequency curves were normal in the three youngest trees. 2. The physical characteristics of the four trees also were determined. 3. The relationships between tree age and mean blade area per tree, mean blade area per class per tree, mean blade fresh weight per tree, crown surface per tree, crown volume per tree, ratio of crown surface to crown volume per tree, trunk diameter per tree, total leaf area per tree, and total leaf number per tree can be expressed by an equation of the general type y = bxn, where x is time. 4. The relationships between tree height and crown diameter, crown surface, crown volume, ratio of crown surface to crown volume, trunk diameter, total leaf area, and total leaf number per tree can be expressed by the allometric equation y = bxk. 5. The relationships between dimensions of plant parts, such as mean blade area per class per tree and blade length, and between these dimensions and other characteristics, such as mean blade fresh weight per class per tree and blade length, crown surface per tree and crown volume, trunk diameter and crown volume, total leaf area per tree and crown volume, and total leaf area and trunk diameter could be expressed by the allometric equation y = bxk. 6. The relationship between mean blade area per class per tree and blade fresh weight was linear and could be expressed by the equation y = a + bx. 7. The relationship between trunk diameter and total leaf area could be expressed more precisely by the exponential equation y = aebx than by the allometric equation. 8. As the Valencia orange tree ages, its shape changes and the shape of its leaves changes. The number of leaves increases more rapidly with age than does any other above-ground characteristic of trees. Mean leaf-blade area per tree and mean leaf-blade fresh weight per tree decrease with the age of tree. Part II.-1. The power function effectively described leaf-blade area in terms of blade length for four varieties of citrus. 2. The allometric coefficient was largest for Valencia orange leaves, and it varied with the age of the tree from which they were picked. 3. The allometric coefficient was distinctive for leaves of each variety of citrus: In Valencia orange n3 = 1.851-1.982, in grapefruit n3 = 1.789, in lemon n3 = 1.784, and in Washington Navel orange n3 = 1.713.

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