Leaf Angle

Tsvetoukhine (1960) separates leaves into horizontal and angled, the angle of which can be best assessed on small leaves near the tip of the stem. The angle varies among clones and to some extent with position on the plant. 

FIGURE 4.2 The margins of the leaves vary widely among clones, with most being serrate, serrate-dentate, or serrulate. Individual teeth point toward the apex and vary substantially in height, frequency, shape, and consistency. (Redrawn from Tsvetoukhine, V., Ann. Amelior. Plant., 10, 275-308, 1960 Kays, unpublished data.) 

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Leaf angle (La) Angle of the leaf from horizontal in degrees 0-55° Lemeur, 1973... 

Figure 9-7. Variation in leaf angle and hence foliar absorption coefficient with distance above the ground for (a) various idealized plants and (b) sugar beet measured at various canopy positions (Hodariova, 1979). Hie greater erectness of the uppermost leaves leads to a lower k for them and hence to better penetration of PPF down to the lower leaves.

Winter, S. R., Leaf Angle Source-Sink and Detasseling Studies with Corn... 

Lovelock CE and Clough BF(1992) Influence of solar radiation and leaf angle on leaf xanthophyll concentrations in mangroves. Oecologia 91 518-525... 

For species that occurred in both light environments leaf angle was considerably steeper in the open versus understory (Fig. 1). Mean leaf angle for Populus tremuloides in the open and understory were 58.2 and 37.9°, respectively, and 33.9° and 16.9°, respectively, for Mahonia repens. Rumex densiflorus did not grow in shaded habitats. 

Figure 1. Frequency distributions of leaf angles (0 horizontal) for Populus tremuloides, Mahonia repens, and Rumex densiflorus. Measurements were made on plants growing in the forest understory (filled bars) or in an adjacent opening (striped bars).

The effect of surfactants on spray retention efficiency is influenced by droplet size and velocity, leaf angle, and surfactant type and concentration. Examination of spray retention and surface spreading on a range of outdoor-grown crop plants was examined by Anderson et Retention was determined by dynamic surface tension, whereas droplet spreading was related to equilibrium values. They concluded that the basis of selection could be determined by cost, lack of phytotoxicity, and ability to solubilize or aid penetration of the a.i. this would not prejudice the retention properties of the formulation. 

To find the equilibrium form of a crystal, the following Wullf construction [20] can be used, which will be explained here, for simplicity, in two dimensions. Set the centre of the crystal at the origin of a polar coordinate system r,6. The radius r is assumed proportional to the surface tension 7( ), where 6 defines the angle between the coordinate system of the crystal lattice and the normal direction of a point at the surface. The anisotropy here is given through the angular dependence. A cubic crystal, for example, shows in a two-dimensional cut a clover-leaf shape for 7( ). Now draw everywhere on this graph the normals to the radius vector r = The... 

AXIL.—Angle formed by leaf or bract with stem or branch or by branch... 

Figure 4.13 Wetting versus nonwetting, (a) The water drop on a lotus leaf with hydrophobic surface leadingto a large contact angle [204]. (b) The water drop on a glass surface with hydrophilic properties leading to a small contact angle [205].

Leaf azimuth angle Leaf direction relative to north (360°) Varies ... 

Leaf zenith angle Angular distance between the leaf and the sun Varies ... 

Examination of the relevant theory indicates that the adjuvant effect of surface-active agents on herbicide action is maximized when the quantity FI = yL cos 0, or the film pressure at the liquid/solid interface, has a maximum value. Measurement of surface tension of 1.0% aqueous solutions and of contact angle on a number of substrates (Teflon, paraffin) and plant-leaf surfaces (soybean, com) as a function of hydrophile-lipophile balance show at least one maximum, and these values are in good agreement with earlier experimental data on herbicidal activity. 

The actual area of the leaf which is covered by a given retained spray droplet will be a function of the spreading coefficient and ultimately the contact angle. Evans and Martin (5) have shown empirically that the area covered by the drop is given by ... 

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